OSSEOUS SYSTEM OF MAMMALIA. 311 



nomena of the head neither supersede nor can supply the better 

 evidences of homology afforded by relative position and connec- 

 tions any more than do those of the foot. The cannon-bone of 

 the ox is developed from three terminal and two middle centres 

 of ossification ; but embryology does not show which of these 

 signify bones distinct in other Mammals : it is neither here nor 

 elsewhere the criterion of homoloixy- Iii the foreo-oinoc account 

 of the Mammalian modifications of the Vertebrate skeleton, the 

 general and serial homologies are given, as determined in my 

 work on the Vertebrate Archetype. But as a few of the special 

 homologies of cranial bones are still unaccepted by fellow-labourers 

 in this field of anatomy, I offer the follomng remarks in excuse 

 for the retention of my opinions on such moot-points. 



To rightly determine the cranial bones in Mammals, as in 

 Birds, we must pass to their investigation from the previously 

 determined bones in the skull of an inferior Vertebrate. Thus, 

 placing the skull of a young Ostrich or Apteryx, showing the 

 sutures, by the side of that of the Ioav, bird-like Monotreme 

 {Echidna,^g. 197), we find that the transversely extended, medially 

 notched occipital condyle, in the Bird, fig. 27, has become bisected 

 or divided into two in the Mammal, fig. 202 ; each moiety being 

 developed wholly (^jEchicbia) or in great part (some Cetacea) from 

 the exoccipital, 2. The basioccipital either wants, or developes 

 only the lower end of, the divisions of the occipital condyle. The 

 exoccipital, in most Mammals, sends ofFa ^paroccipital ' process, 4, as 

 in Birds. The basi-, ex-(2), and super-(3)occipitals coalesce into one 

 bone, but rarely are fused, as in Birds, with the sense-capsule and 

 segment in advance. The basisphenoid, fig. 202, 5, differs from that 

 of the Bird, figs. 27, 32, in not being coossified with the presphenoid, 

 9 : laterally it contributes to form part of the otocrane and tym- 

 panum, in advance of which it articulates with the alisphenoid, figs. 

 196, 197, 6. In the Echidna a bone, fig. 197, 8, coossified with or 

 anchylosed to the outside of the petrosal, expands beyond it to arti- 

 culate with the ex-(2) and super-(3)occipitals, with the parietals, 7, 

 and the alisphenoids, 6. This bone, in many other Mammals, deve- 

 lopes a ' mastoid ' process, as in Birds : it is developed, as in them, 

 in and from the lateral cranio-cartilage enveloping the otic capsule : 

 it is plainly the homologue of 8 in the Bird, fig. 196. Between 8 and 

 6 in Echidna there is a vacuity in the bony .skull. The parietal, 7, 

 is relatively larger, the frontal, ii, is smaller, than in the Bird. 

 The nasal, 15, is simply elongate, in Echidna as in Rhea, : it does 

 not bifurcate anteriorly by sending down a maxillary prong or pro- 

 cess as in the Ostrich, fig. 196, 15, and most Birds : but it is longer 



