COMPARATIVE ANATOMY. 



entirely absent, and the two hemispheres 

 united throughout in one mass, without 

 any perceptible inconvenience during the 

 patient's life. (" Transactions of a So- 

 ciety for the Improvement of Medical 

 ana Chirurgical knowledge," vol. ii. p. 

 212.) We have met with four instances, 

 in which the anterior half of the falx 

 was deficient. This production of the 

 dura mater commenced in a narrow form 

 about the middle of the sagittal suture ; 

 and gradually expanding, had acquired 

 the usual breadth at its termination in the 

 tentorium. The two hemispheres ad- 

 hered by the pia mater covering their 

 opposed plane surfaces, but were form- 

 ed naturally in other respects. A want 

 of the falx has also been recorded by 

 Garengeot, (" Splanchnologie," torn. ii. 

 p. 24.) 



The brain of the mammalia wants the 

 digital cavity of the lateral ventricle, and 

 in general the acervulus of the pineal 

 gland. Its anterior lobes are elongated 

 into a process called ihe mammillary, giv- 

 ing rise to the olfactory nerves. In birds, 

 reptiles, and fishes, there is a successive 

 and gradual change towards a more 

 simple structure ; the brain in these 

 classes consisting merely of tubercular 

 eminences. In the lower orders the 

 brain seems to be really wanting. A 

 nervous chord runs along the body, and 

 possesses ganglia at different distances, 

 from which the nerves arise. In insects 

 and vermes the upper ganglion of the ner- 

 vous chord, which represents the brain, 

 is placed near the mouth, or oesophagus, 

 and very generally surrounds that tube 

 by a kind of collar. 



ORGANS OF SENSE. 



Few subjects in comparative anatomy 

 and physiology have given rise to more 

 various and contradictory opinions, than 

 the organs of sense in some classes of ani- 

 mals. Much misunderstanding on this 

 point has clearly arisen from the incon- 

 siderate and unconditional application of 

 inferences drawn from the human sub- 

 ject to animals. Thus it has been sup- 

 posed that those which possess a tongue 

 must have it for the purpose of tasting, 

 and that the sense of smell must be 

 wanting, where we are unable to ascer- 

 tain the existence of a nose. Observa- 

 tion and reflection will soon convince 

 us, that the tongue, in many cases (in 

 the ant-eaters among the mammalia, and 

 almost universally in birds,) cannot, from 

 its substance and mechanism, be consider- 



ed as an organ of taste ; but must be 

 merely subservient to the ingestion and 

 deglutition of the food. Again, in several 

 animals, particularly among insects, an 

 acute sense of smell seems to exist, al- 

 though no part can be pointed out in 

 the head, which analogy would justify us 

 in describing as a nose. 



However universally animals may pos- 

 sess that feeling which makes them 

 sensible to the impressions of warmth 

 and cold, very few possess, like the 

 human subject, organs exclusively ap- 

 propriated to the sense of touch, and ex- 

 pressly constructed for the purpose of 

 feeling, examining, and exploring the 

 quahues of external objects. 



This sense appears, according to our 

 present state of knowledge, to exist only 

 in three classes of the animal kingdom ; 

 ixz. in most of the mammalia, in a few 

 birds, and probably in insects 



The structure of the organ of touch is 

 the most perfect, and similar to that of 

 the human subject in the quadrumana. 

 The ends of their fingers, particularly of 

 the poster! or extremities, are coveredwith 

 as soft and delicately organized a skin as 

 that which belongs to the corresponding 

 parts of man. 



Several of the digitata are probably pro- 

 vided with this sense ; the organization 

 of the under surface of the front toes of 

 the raccoon (ursus lotor,) and the use 

 which the animal makes of those parts, 

 prove this assertion. 



It is not so clear that we are author- 

 ised in considering the snout of the mole 

 and pig, not to mention the tongue of th? 

 solidungula and hisulca, or the snout of 

 these and other animals, as true organs 

 of touch, according to the explanation 

 above laid down. 



Much less can we suppose the long 

 bristly hairs, which constitute the whiskers 

 of the cat-kind, and other mammalia, to 

 be organs of touch, in the sense we are 

 now considering, although they may be 

 serviceable, when they come in contact 

 with any object, in warning, and making 

 the animal attentive. Bats have been 

 supposed to possess a peculiar power of 

 perceiving external objt cts without com- 

 ing actually into contact with then. In 

 their rapid and irregular flight amidst 

 various surrounding bodies, they never 

 fly against them? yet it does not seem 

 that the senses of hearing, seeing, or 

 smelling, serve them on these occasions; 

 for tlv-y avoid any obstacles with equal 

 certainty when the ear, eye, and nose, are 

 closed. Hence naturalists have ascribet*. 



