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HARDWICKE'S SCIENCE-GOSSIP. 



[May 1, 1S70. 



at the epiglottis— that lump which is popularly 

 known in man by the name of Adam's apple. After 

 detaching it in its course down the neck, which is 

 easily done, it must be pushed through into the 

 thorax, and seized with the forceps with the left 

 hand, and with the assistance of the knife the attach- 

 ments of the heart to the chest separated. In a few 

 moments you will be able to draw it out uninjured, 

 flanked by the lungs, and with the trachea rising 

 from the centre. Dissecting this will be a charming 

 occupation. You should notice whence the aorta, 

 or great artery, starts, where the arteries branch 

 forth to supply the head, where the vein enters carry- 

 ing back the impure blood, and the arteries which 

 carry the blood to the lungs to be purified, and the 

 viens which return it to the heart. Next examine its 

 structure : its four compartments ; right and left 

 auricle and right and left ventricle ; its valves, 

 muscular coats, and ligaments; the bifurcation of the 

 trachea to each lung ; the numerous branches of the 

 bronchi ; the structure of the trachea and of the epi- 

 glottis. If ail this were done thoroughly, it would 

 afford the dissector many hours of delightful study. 



The viscera being disposed of, the head must now 

 receive your attentiou. Here there are both mus- 

 cles and nerves, veins and arteries to be dissected 

 out, without destroying them all in the act. And 

 this being impossible, it is necessary to select one or 

 other of these points and. sacrifice the rest. If the 

 specimen is a kind of which you can get several with 

 ease, you may devote one to each particular ; but if 

 it is a rare and unusual animal, the muscles bear 

 the most importance. Investigating these is a 

 laborious undertaking. You must carefully dissect 

 away until you pretty well detach each muscle from 

 its fellows along its entire length. You must then 

 note its origin, or, in other words, from whence it 

 takes its rise ; its insertion, or where it goes to. 

 Then its use must be determined. This may partly 

 be done by observing what two portions of the frame 

 it connects, and partly by pinching and irritating the 

 muscle, when it will contract as it did when insti- 

 gated by the brain. Those governing the compli- 

 cated movements of the jaws and the neck will be 

 traced with interest. 



In the fore-leg or arm the same plan must be fol- 

 lowed ; often by pinching its muscles you may make 

 the paw suddenly close up, clenched as if in defiance. 

 The muscles of the hind-leg having been likewise 

 identified and separated, you may proceed to the 

 examination of the nerves of the opposite fore-leg, 

 tracing them from their source and disentangling 

 them from their course among the muscles. The 

 second hind-leg may be devoted to the observation 

 of the veins and arteries ; the former having valves 

 opening upwards, and the blood in them of a darker 

 colour than that which is in the latter. It must be 

 kept in mind that the connection betweenthe arteries 

 and veins is by capillaries, which are hair-like vessels 



invisible to the naked eye. It would be a delightful 

 exercise to devote an entire animal exclusively to 

 the circulatory system, tracing from the heart the 

 arteries spreading to the head, body, and legs, and 

 the veins returning it from all these diverse parts 

 again to the heart. It is best to select a moderate- 

 sized specimen for this, siuce then, if a vessel is cut, 

 the amount of escaped blood is not so great. 



In small animals little can be done to the eye; but 

 in large ones, such as the sheep or the ox, there is 

 perhaps nothing that will give more delight. The 

 purity of the vitreous and aqueous humours ; 

 their peculiar semi-firm and semi-fluid consistency; 

 the beautiful blackening of the middle coat ; the 

 lens, the retina, and the exit of the optic nerve to 

 the brain, are all objects of admiration. The eye 

 must first be extracted from its socket, its security 

 in which is astonishing. There is little fear, how- 

 ever, of piercing it, as its consistency is correspond- 

 ingly great. 



The dissection of the ear is attended with great 

 difficulty, as all its important parts are lodged in the 

 temporal bone, and it would be useless to attempt 

 here to give any directions on the subject. 



When you have traced the connection of the nose 

 with the mouth, the cleft of the nostrils, their pitui- 

 tory glands, and the fine network of nerves spreading 

 over.their delicate surfaces, you may proceed to the 

 brain. This may be got at by carefully sawing 

 asunder the skull at the jointure between the two 

 parietal bones, care being taken not to cut and injure 

 the delicate substance below. Then observe that 

 it is divided into two separate portions,— the upper 

 brain, orcerebrum, and thelower brain, or cerebellum; 

 that the great spinal nerve proceeds from the little 

 brain, or cerebellum ; that the cerebellum is formed 

 of two hemispheres; that it is convoluted in structure, 

 whilst the cerebellum is in layers, or laminated ; that 

 nerves branch off through little apertures in the skull 

 to the eyes, nose, ears, mouth, and so on; and that the 

 two hemispheres of the .brain are subdivided into 

 smaller lobes. The spinal nerves branching from 

 the great cord, with the two roots to each, — the one 

 the root of the nerve of motion and the other the 

 root of the nerve of sensation — should be observed 

 and followed. 



The soft part of the animal frame is now finished, 

 and the skeleton alone remains. But this in itself 

 would take a separate article to demonstrate. 



Cutting oneself whilst dissecting often turns out 

 a very serious affair, and great care must be taken 

 to avoid it. The most efficient remedy is to suck 

 the wound, and then to hold the finger for some time 

 in cold water, and not to take too rapid measures to 

 arrest the bleeding. 



Cautioning the anatomist to persevere, I wish 

 him good speed in the cheery and sunny path of 

 comparative anatomy. 



Booton. Edward Fentone Elwin. 



