176 MB. H. G. SEELEY ON OSSEOUS RESEMBLAKCES 



poises and Armadillo. Except, however, with the Porpoises and 

 Mau, a mammal rarely admits the maxillary bone into the border 

 of the anterior nares, as do Chelonians. 



Except in certain Rodents, some Monkeys, and Man, those 

 mammals which have the orbit for the eye surrounded with bones 

 do not admit the maxillary bone into its border, as is usual with 

 Chelonians. The lateral eyes and terminal nostril are mamma- 

 lian ; but only in Man are the similarly placed premaxillaries so 

 small. 



Certain Carnivora have the parietal and supraoccipital bones 

 elevated into a median crest, but it is never prolonged so far 

 backward as among Chelonia. 



The essential difference between the mode of union of the skull 

 with the vertebral column is made by the forward recession among 

 mammals of the basioccipital element. 



The forms of Chelonian ribless cervical vertebrae may be par- 

 alleled in mammals. The testudinate group has its analogues 

 in such long-necked forms as the GrirafFe and Llama. The ma- 

 rine group has more the proportion of the neck-vertebrae in 

 the Sheep ; but there is a stronger hypapophysis, and only an 

 indication of the transverse process characteristic of short-necked 

 mammals. The opisthocoelous feature of the earlier vertebrae 

 is a character of ruminant mammals. 



The dorsal ribs have a mammalian character in articulating 

 between the bodies of two vertebrje, though they usually diflfer 

 in appearing to have no union with the neural arch. When, 

 as with the Armadillo, a mammal is covered with an osseous 

 sheath, it is not homologous with that of Chelonians, being merely 

 dermal, and having no osseous union with the skeleton. 



The tail in the marine and testudinate groups agrees with most 

 mammals in wanting the chevron bones ; but all Chelonians differ 

 from mammals in having the neural arch prolonged to tlie end of 

 the tail. 



The pectoral arches are dissimilar. 



The curves in the mammalian humerus appear at first sight to 

 be the reverse of those in the Testudinata, owing to the bone being 

 directed forward instead of backward, so that the left humerus of 

 one type resembles the right humerus of the other. The bone 

 corresponds most closely in form with that of Seals, which in 

 common with many Carnivora, have a similar hemispherical liead 

 and a similar foramen on the inner and lower border of the shaft. 



