Part I

In our desperate need to find answers we often rely on skeletal remains to tell their tales of origin and fate. Physical anthropologists have too long concentrated on ostoelogical factors to draw conclusions or propose newer theories on the origins of the man.

Today, science, delving deep into genetics and other nascent specialties, has made anthropological studies easier, and perhaps more reliable. Yet, one often wonders, whether we are ignoring any telltale evidences of evolution, often manifest in us and around us. In my line of work, as a teacher of human anatomy to medical students, I have often stumbled upon an odd anatomical feature or two, that seemed quite out of place in the utopian functional design and efficiency of the highest form of evolution, man. Take for example, the lachrymal (lacrimal) apparatus…

Some years ago, observing my pet dog, attempt to dislodge a foreign body from it’s own eye, I saw, fascinated, a unique maneuver that promptly expelled the offending alien particle. The dog, just used its front paw to shut the edge of one side of its nose and nostril, and induced a sneeze, which in turn, expelled the foreign body. Intrigued, I experimented again and again with the animal and in some others too, then on my friends (all medical students). In every case, shutting of the contralateral nostril (the left, if the foreign body is in the right eye), and inducting a sneeze, dislodged any superficially located particle. So effective and noninvasive was the procedure, that I even reported it in a medical journal as a simple first aid procedure

Over the years I have off and on recommended the procedure even in patients with chronic dachrocystitis, and epiphora. The maneuver repeated over a time, clears the lacrimal ducts and restores their patency, often non-surgically. Now what has all this got to do with evolution you may wonder? It does, I think.

I have since dissected the lachrymal sac in a number of human cadavers, and studied them grossly as well as microscopically. The apparatus consists of two minute canals, which originate at the upper and lower lid’s medial edge. Each canal then takes an abrupt angulation, to converge towards its fellow duct. Here they open into a fusiform sac, which in turn, open ended (bottomless, except for a flap of mucous membrane) caudally to open directly into the lateral wall of the nasal cavity. The ducts convey secretions produced by the lacrimal gland, which bathes the corneal surface of our eye. The secretion, is a oil-watery saline, which acts as a moisturizer and sterilizes the exposed eye surface.

Physiologically, in man at least, the gland has little other function, excepting as an ineffective aid to excretion of salts. The question is, why would nature design such a complicated apparatus for something which performs so little, function wise? Nature does not condone waste in investment. Is the lacrimal sac performing some other role in man? For that, the answer is found in the quadrupeds, as I found in my dog.

So what is the role of the sac? A dilated balloon, made up of fibro-elastic tissue (Elastic?!! Why !!!??) Why should the sac wanna recoil? from what? for what?

The spent secretions of the eye are transported by the canals into the sac where it pools up, wherefrom it percolates into the nose to dry up with the warmth of the inspired air. But why is nature storing this waste? A few droplets of lacrimal secretion is held within each sac, which has a simple flap valve at its lower end (an ineffective valve at that!) Now let me assume I am a dog (or a donkey maybe, as many of you would be tempted to suggest!). I have this irritating particle that flew into my eye, so, I presto, shut my left nostril, sneeze….and in the process increase my intranasal pressure, which increase flips open the valve at the caudal end of the sac, which then is subject to some intense reverse pressure, reacting to the stress by violently contracting its elastic components. This contraction shuts the valve, and forces the sac stored lacrimal fluid back along the ducts, in a reverse flow. The fluid now jets out off the punctae at the medial edges of the eyelid…the jet stream of saline washes across the cornea like a windscreen wiper and flushes out the foreign body from the eye.

Aha! So thats the function of the lacrimal apparatus. Then why isn’t man using the manouvre himself? Hmmm.. …That is because he’s turned biped pal!! (now, it’s my turn to call you names!)

Hold it buddy, what’s bipedalism doing here?
The lacrimal apparatus’s efficiency is severely compromised by our erect posture and the reverse pressure required by man to flush back fluid from his sac up the eye is enormous and strenuous: But in a quadruped, a cinch! The sac lies an easy sloping antigravity level, a small sniff or sneeze does the trick; in us, we need to try harder, but it works. Try sniffing some snuff, and watch how forcefully you sneeze, and how so much fluid gushes and brims your eye. Try with one nostril shut if you must.

So what does all this show? That maybe, bipedalism has not only changed the way eye things foreign, but has also changed the way we deal with foreign bodies in the eye. In our evolutionary hurry to go biped, we have lost out a very important and useful function of one of our old friends, the lacrimal sac. Now the poor sac, is just used to fill excess tears of a sobbing session.

What is the fate of the gland and sac now? Will it regress or become atavistic in years to come and go the way of our appendix or caudal appendage? I sincerely hope that we rediscover the potential of the lacrimal gland and its original function, and use a sneeze to expel any foreign body…and thus pay our dues to the machinations of evolutionary compromise. If not, R.I.P. Lacrimal Apparatus Sac & Gland, I will miss you. Sob sob, sniff sniff. If you have tears, prepare to shed them now.

Part II

Watch the ‘mum to be’ walk. Ungainly, tipping over gait, with the third trimester foetus pushing against her anterior abdominal wall, stretching the muscles to tautness. Look at her as she carefully weaves her way in that insanely narrow aisle at the supermarket, careful mum, that shopper yonder seems to be in haste as she careens ahead erratically towards her. Then just in the nick of time, a collision is averted, a deft sidestep….and the oncoming peril is averted. It is not the evasive side-stepping maneuver of the mum to be that gets me curious, it is another instinctive action she takes to protect her unborn baby. She has hastily removed both her hands from the shopping cart, and folded her elbows defensively on her abdomen, her wrists flex and digits curl.

Flexion is a natural mechanism, the first line of defense against perceived dangers. Watch how the caterpillar curls itself, or that pangolin. Or any quadruped for that matter. Universal flexion, every joint in flexion, is used to protect every vital organ in the abdomen, pelvis, or thorax, against assault. Why even the growing foetus in that mums womb, is in a position of universal flexion. But our ‘mum to be’ just has to make do with just two forearms flexed against her abdomen as her only line of defence. Ever wondered why?

The answer is evolution. With the emergence of Homo erectus, the additional flexion-induced protective shield available from the two lower limbs has been lost to the bipedal human. Were she still a quadruped, sighting the oncoming peril at the mall, our mum would have squatted, or crouched, and drawn her knees up close, in complete flexion along with the hip, the vertebral column itself would have flexed through contraction of the abdominal recti…but now, she just has to stand erect, the product of seven months of gestation, exposed to any, or all elements that threaten frontally.

In another article, written for this site (‘Shedding a tear for bipedalism’) I had discussed how I felt that the human lacrimal gland, and more particularly the apparatus appended to it, was slowly becoming functionally insignificant thanks to erect posture and our two- legged mobility attribute. The question I raise now is, could not the partial loss of protective flexion, with specific reference to the ‘mum to be’ analogy cited, be wholly attributed to the acquisition of bipedal gait and erect posture? Is the modern Mrs. Eve paying the price for a decision her ancestor, Mrs. Lucy took three million years ago, to move on in life, and up the evolutionary ladder, on two, not four limbs?

Should another tear ready to be shed for ‘bipedalism’? Is the time tested reflex of ‘universal flexion’ being shoved out of our lives? Evolution took away my appendix, my platysma, my pyramidalis, and my auricular muscles.. It docked my tail. It has compromised the capabilities and range of flexion in the gravid human female…what next? Pardon me mate, I must shed some tears, right away, for turning biped and erect. Pass another tissue please, quick, before evolution deletes my even that tear shedding function of my lacrimals, totally.

Sources:

Arunachalam Kumar,1982,More nose blowing for foreign body removal
Canadian Family Physician, Vol. 28, No. 2, 198

Prabhu LV & Arunachalam Kumar, 2003, The Functional anatomy of the Lacrimal sac, Karnataka Journal of Ophthalmology, Vol.20, No.2, 26-27

Ganesh KC, Arunachalam Kumar, Nayak SR et al, 2009, Morphology of the lacrimal sac and nasolacrimal duct in adult human cadaver
Bratislava Medical Journal(in press)

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