400 



Prof. Huxley on the 



[Mar. 6, 



reduced to a mere slit, often bridged over by a process of the ischium.* 

 The pectineal process is immensely elongated in some Ornithoscelida 

 (as Hnlke has shown in Iguanodon, and Marsh in Laosaurus (Plate 8, 

 fig. 8)); but, in birds, it is usually short (fig. 9), and may be absent, 

 and no epipubes have been discovered, either in the Ornithoscelida 

 or in birds. f 



Thus, it appears to be useless to attempt to seek among any known 

 Sauropsida for the kind of pelvis which analogy leads us to expect 

 among those vertebrated animals which immediately preceded the lowest 

 known Mammalia. For, if we prolong the series of observed modifica- 

 tions of the pelvis in this group backwards, the " Promammalia " 

 antecedent to the Monotremes may be expected to have the iliac and 

 obturator axes perpendicular to the sacral axis, and the iliopectineal 

 axis parallel with it ; something, in short, between the pelvis of 

 an Ornithorhynchus and that of a land tortoise ; and provided, like the 

 former, with large epipubes intermediate in character between those of 

 the lower mammals and those of crocodiles. In fact, we are led to 

 the construction of a common type of pelvis, whence all the modifica- 

 tions known to occur in the Sauropsida and in the Mammalia may 

 have diverged. 



It is a well-known peculiarity of the urodele Amphibia, that each os 

 innominatum consists of a continuous cartilage, the ventral half of which 

 is perforated by a foramen for the obturator nerve, but has no large 

 fibrous fontanelle, or obturator foramen, in the ordinary sense of the 

 word. At the junction of the dorsal with the ventral moiety, the aceta- 

 bulum marks off the iliac portion of the pelvic arch above, from the 

 pubic and ischial regions below; and these are further distinguishable, 

 even apart from their ossifications, by the position of the foramen for the 

 obturator nerve and the origins of the muscles. In full-grown specimens 

 of Salamandra maculosa, the pelvis presents the following characters 

 (Plate 8, figs. 1, 10, and 11) : — The iliac axis is slightly inclined for- 

 wards, while the iliopectineal axis is practically parallel with the sacral 

 axis. The iliac ossification extends into the acetabulum, and forms a 

 triangular segment of its roof with the apex downwards, exactly as in 

 lizards. The posterior and inferior side of the triangle is separated by 

 a thin band of the primitive cartilage from the upper edge of the simi- 

 larly triangular cotyloid end of the ischial ossification, the anterior edge 

 of which is vertical, again as in lizards. Between this edge and the 

 anterior and inferior edge of the iliac ossification there is a cartilagi- 



* I was, at one time, inclined to think that this represented the union of the 

 pubes and ischia of the same side in ordinary Sauropsida, and that the rest of the 

 ischium represented an unusually elongated metischial process ; but the study of 

 the development of the pelvis in the chick has convinced me that this is not the case. 



+ See, however, the observations of Mr. G-arrod on a " marsupial bone " in 

 ostriches. "Proceedings of the Zoological Society," 1872. 



