584 CETACEA. 



anterior part of the vermiform process of the size, as the third (3), the fourth (4), and the 



cerebellum. sixth (6) pair. 



The pineal gland is a small flattened body The fifth pair (5), which emerge from the 



about two lines in length, connected as usual sides of the pons, but arise from the medulla 



to the thalami optici. These appear in each oblongata between the corpora restiformia and 



ventricle in the form of an oval flattened olivaria, have a smaller proportional size than 



body (i, Jig, 273). They are joined together in man. 



posteriorly by the medullary commissure. The nerves concerned in the actions of 



Tiedemann did not observe any soft commis- respiration, as the facial (7), the pneumogastric 



sure. (10), and the recurrent (11), are well deve- 



The third ventricle is continued anteriorly loped, in relation to the large size of the 



into the infundibulum. muscles which effect the respiratory movements 



The corpora striata (c?) are proportionally of in the dense medium of water, 



small size, as Hunter observed in the brain The glosso-pharyngeal nerve (9) and the 



of the Whale. They are united anteriorly by lingual (12) are also very large, corresponding 



the anterior commissure. to the vigorous associated actions of the tongue 



The fornix is also of inconsiderable size, and pharynx, which must take place during 



The slender anterior pillars of the fornix proceed deglutition in the Cetacea. 



to the mammillary bodies, and send forwards But perhaps the most remarkable nerve for 



two small triangular medullary lamellae to the its great relative size is the acoustic (8), which 



under surface of the anterior part of the corpus certainly testifies to the delicate sense of hear- 



striatum, from which the septum lucidum is ing in the Dolphins.] 



continued. The fornix then bends backwards The organs of the senses, with the exception 

 along the under surface of the corpus callosum of that of smell, are composed, in all the 

 and above the thalami, and its hinder crura Cetaceans, of the parts which essentially con- 

 sink down, diverging from each other to form stitute them in terrestrial Mammalia, and are 

 the cornua ammonis (g). These bodies are only modified with reference to the habitually 

 small, thin, but broad, and exhibited no den- aquatic life of the animals of this order. But 

 ticulated folds. The taenia fimbriata (A) are little inquiry has been made as to their utility 

 attached as usual to the external border of the in these animals, the length of time they con- 

 cornua. tinue serviceable, and the characteristic diflfe- 



The lateral ventricles are capacious though rences which might be drawn from them for 

 short; they extend, as in the human brain, the distinction of the species, 

 into an anterior, a middle, and a posterior horn ; Eye. The eye of the Herbivorous Cetaceans 

 the latter, however, is very small. In each alone is provided with a lateral lid or membrana 

 ventricle there is a large plexus choroides, which nictitans; that of the Spouting Whales is de- 

 is remarkable for the transverse parallel folds void of lachrymal glands; but its lids are fur- 

 of membrane which support the divisions of nished below with little glands which secrete a 

 the artery. mucous matter, adapted like the tears for 



With respect to the cerebral nerves, Tiede- lubricating the sclerotica. 



mann states that, although in the Dolphin the [Hunter observes that " the eye in this 



brain was removed with every precaution from tribe of animals is constructed upon nearly 



the skull, yet he could not perceive the slightest the same principle as that of quadrupeds, dif- 



trace of the olfactory pair. Hunter and Tyson fering, however, in some circumstances ; by 



equally failed to detect them in the Porpesse. which it is probably better adapted to see in 



Treviranus, however, believed that with the the medium through which the light is to pass, 



aid of a magnifying glass he had detected very It is upon the whole small for the size of the 



delicate filaments in the situation of the olfac- animal, which would lead to the supposition 



tory nerves in the Porpesse. But supposing that their locomotion is not great; for, I believe, 



that there was no illusion here, which could animals that swim are in this respect similar to 



hardly have happened to so accurate and close those that fly ; and as this tribe come to the 



an observer, these fibres represent only a very surface of the medium in which they live, they 



rudimental condition of the olfactory nerves ; may be considered in the same view with birds 



and we may observe that the shortness of the which soar ; and we find, birds that fly to 



anterior lobes of the brain, and the smallness great heights, and move through a considerable 



of the striated bodies are closely related to the space, in search of food, have their eyes larger 



absence or imperfect development of the first in proportion to their size, 



pair of nerves. " The eyelids have but little motion, and 



With respect to the other cerebral nerves, do not consist of loose cellular membrane, as 



they are relatively larger in proportion to the in quadrupeds, but rather of the common 



brain than in man. The optic nerves (2, fig. adipose membrane of the body ; the connexion, 



272) rise partly from the thalami, partly from however, of their circumference with the com- 



the anterior bigeminal bodies and the corpora mon integuments is loose, the cellular mem- 



geniculata; they curve round the crura cerebri, brane being less loaded with oil, which allows 



and unite as usual before the pituitary gland, of a slight fold being made upon the sur- 



The angle at which the nerves diverge from rounding parts in opening the eyelids. This 



each other after the decussation is more open is not to an equal degree in them all, being 



than in other Mammalia. less so in the Porpoise than in the Piked 



The accessory nerves of the eye are of large Whale. 



