Prof. Eschricht on the Gangetic Dolphin. 185 



and Vrolik*, Owenf and Maclise J. The ribs as well as trans- 

 verse processes are to be considered collectively as fragments of 

 common visceral or ventral arcs^ each of which, in its complete 

 state of development, has a twofold origin, or two roots : 1st, the 

 ventral, from the body of the vertebra; and 2nd, the dorsal, 

 from its arc (neurapophysis). The cervical transverse processes 

 are the complete roots of visceral open arcs (that is, not reaching 

 the medial line of the abdomen) . The anterior thoracic arcs are 

 always the most complete; their middle part (body of the rib) 

 is connate with the ventral root (the neck and head of the rib) 

 which is detached from the vertebra (in the Balanoptercs this root 

 is quite tendinous or cartilaginous) ; the dorsal root (processus 

 transversales), on the contrary, being connate with the vertebra, 

 but detached from the middle part (the rib). In the series of 

 thoracic vertebra3 the two roots approach, and at last melt into 

 each other (in the ninth in the Gangetic dolphin) at the point 

 of transition between the arc and the body, the connate part of 

 the arc (the transverse process) becoming at the same time pro- 

 portionally shorter. In the last thoracic vertebrae (the tenth and 

 eleventh in the Gangetic dolphin) it again increases in length, 

 continuing in the lumbar vertebrae, but only as a ventral root (pro- 

 ceeding from the body of the vertebra), the arc portion is wanting 

 altogether. The last pair of ribs is, therefore, exclusively at- 

 tached to the transverse processes seated on the body of the ver- 

 tebra ; but these processes cannot be considered as homologous 

 with those of the first thoracic vertebrae, but much rather with 

 the necks and heads of the ribs. 



On the other hand, if we compare the last caudal vertebrae 

 with the lumbar, we shall find their difference not less marked, 

 than what exists between the latter and the cervical vertebrae. We 

 designate as the first caudal vertebra, that behind which is situated 

 the foremost haematapophysis (Cuvier^s " os en V^^) . It is the 27th 

 in the column, and consequently one of the 33 vertebrae behind 

 the 7 cervical and 12 thoracic ; 8 being designated as lumbar and 

 the last 25 as caudal vertebrae. In M . Reinhardt^s skeleton there 

 are 14 haematapophyses entirely, or in part only osseous; and as 

 the first is situated between the 27th and 28th vertebrae, the last 

 is situated between the 41st and the 42nd. I propose to distin- 

 guish this 42nd, and all the subsequent vertebrae, as extreme 



* Natuur. en Ontleedkundige Beschouwing van den Hyperoodon. Trans- 

 act, in Nat. Hist, of the Dutch Acad, of Sciences at Haarlem, 2 ser. vol. v. 

 part 1. p. 34-40. 1848. 



t On the Archetype and Homologies of the Vertebrate Skeleton. 

 Lond. 1848, 8vo. — On the Nature of Limbs. A Discourse by R. Owen. 

 Lond. 1849. 



X In Cyclopaedia of Anatomy and Physiology ; edited by R. B. Todd. 

 Part XXXV. Article Skeleton. London, 1849. 



