260 
PROFESSORS T. W. BRIDGE ARD A. C. HADDON 
organ encapsuled by bone, but the capsules are perforated posteriorly for the passage 
of two cascal diverticula. 
The Homology of the Weherian Ossieles. 
Excej^t with regard to the intercalarium, our investigations throw no additional 
light on the nature of the Weberian ossicles, and that this is the case is mainly due 
to the highly sj)ecialized character of this mechanism in tlie Siluridm. As far as this 
family is concerned comparative anatomy is of but little use in the discussion of this 
question, and embryology is the only line of investigation which offers any prospect 
of a satisfactory and final solution of the problem. The views of different investi- 
gators on this point are maiidy based on a comparative examination of the condition 
and relations of the ossicles in the less highly specialized Ostariophyseae, and piunci- 
pally in the Cyprinidae. The conclusions of E-amsay Weight and Grassi, however, 
rest on the development of these structures in Amiurus caius (Siluridae) and the Carp 
(Cypiinidae) respectively. The different views may be brieffy stated in the following- 
table : — 
1 
Cliiustrum. 
Sca 2 )liium. 
Intercalarium. 
Tripus. 
Baudelot (1868) . . . 
Neural spine, or 
divided intei-- 
crural bone of 
Neural arch of r.^ 
Neural arch of v.~ 
Transverse pro- 
cess or rib of 
V? 
Nusbaum (1881) . . . 
Neui-al spine of 
M n 
5) 55 
Rib of V? 
Gr.assi (1882) .... 
Part of the skull . 
}) n 
55 55 
Ti'ansverse pro- 
cess of V? 
Ramsav tYRiGHT (1884). 
Nem-al spine of 
5 5 5 5 
55 55 
Sagemehl (1885) . . . 
Part of the occipital 
segment of the 
skull 
51 J5 
Rib of V.- . 
Rib of V? 
Sorensen (1890) . . . 
Neural spine of v.^ 
1) 55 
Neural arch of v.~ 
55 
(t’.h r.“, = the first, second, and third vertebrae.) 
The identification of the intercalarium as the neural arch of the second vertebra 
rests mainly on its condition and relations in certain Cyprinidae. In Cypriims the 
ossicle consists of an articular process which rests on the body of the second vertebra, 
of an ascending process which forms part of the wall of the neural canal, and a 
horizontal process terminating distally in the interossicular ligament. In the light 
of such facts the nature of the intercalarium presents no special difficulty. With tlie 
Silurldoe, however, it is otherwise. In all previously investigated species the inter- 
calarium is represented by a variously shaped nodule of bone imbedded in the inter- 
ossicular ligament, and has no connection with the walls of the neural canal, or with 
