PLATANISTA. 549 



In the first specimen, no ossicles of the first segment of the mesosternum 

 are developed, but in the second and third specimens, the ossicle on the left half is 

 enormously larger than the minute ossicle that lies imbedded in the right half of the 

 cartilage. 



There are distinct indications, on the latter aspect of the mesial sutural line, 

 of the two original elements. The facet for the first rib is borne on a slight 

 projection on the anterior angles and looks backwards and outwards. It is subject, 

 however, to considerable variation. In one specimen the anterior border is nearly 

 straight instead of concave. 



Conclusion. — In bringing this Memoir to a close, I shall briefly summarize 

 the more prominent features of the animal of which it treats. The external 

 characters may be re-iterated thus : a long compressed snout, with a formidable array 

 of teeth ; a vaulted compressed forehead ; longitudinal blow-hole ; scarcely percep- 

 tible eye ; distinct neck ; broad and abruptly truncated pectoral fins and small dorsal 

 fin; and the male, a smaller but heavier- built animal than the female, with a 

 shorter snout. To these may be added the remarkable changes which take place 

 in the teeth and in the curvature of the snout between youth and age. 



The most noteworthy peculiarities in the internal structure of this Cetacean 

 appear to be, the great development of the Eustachian tube and of the large 

 sacs connected wdth it, and which he along the hyoid apparatus ; the remarkable 

 valvular and glandular structure of these sacs, and of their ramifications, only 

 separated from each other in the mesial fine by a thin membrane ; the existence of 

 a peculiar glandular area in the second cavity of the stomach, associated with 

 enigmatical cup-shaped bodies; the apparent natural shedding of the superficial 

 membrane of the first gastric cavity as in some birds ; the chambered character of 

 the small intestine, due to the great development of valvulae conniventes; the 

 existence of a caecum, with which is associated a large gland ; remarkable dilatations 

 in the vascular system of the spleen ; the modifications of the spiracular sacs con- 

 nected with the blow-hole ; the fibrous blubber of the forehead ; the modifications 

 of the laryngeal cartilage ; the broken-up character of the rings of the trachea ; 

 the broad bifid heart ; the abrupt termination in rete mirabile of the branches 

 of the great arteries towards the head, and the anterior extremities ; the simply 

 formed brain, distinguished by moderate breadth and considerable height; the 

 excessively rudimentary character of the optic nerves ; the possible absence of 

 the third and fourth pairs of cranial nerves ; the eye devoid of a crystalline lens 

 and only a rudimentary choroid membrane present; the rudimentary develop- 

 ment of the muscles of the eyeball; the glandular character of the conjunctival 

 covering of the cornea ; the presence of utricular-like glands in the vagina 

 of the gravid female, and the existence of utricular glands in the uterus of the 

 foetus. 



With regard to the skeleton, the great development of the maxillary crests ; 

 the anterior compression and elongation of the maxillaries with the premaxillaries ; 

 the prolonged mandible, with its extended symphysis ; the position of the palatine in 



