THE SKULL. 



83 



the nasal and oral cavities (incisive or naso-palatine canal). In the 

 lateral parts of the face of most Mammals, the jugal or malar 

 connects the maxilla with a process of the squamosal instead of 

 with the quadrate, as in Amphibia and Sauropsida: in Ungulata 



c.n 



FIG. 67. SKULL OF EMBRYO OF ARMADILLO (Tatusia hybrida). (Modified from a 



drawing by W. K. Parker.) 



a.ty, tympanic annulus ; au, auditory capsule; b.hy, hasihyal ; c.hy, ceratohyal ; 

 cr, cricoid ; d, dentary ; c.hy, epihyal ; e.n, external nostril ; co, excceipital ; 

 /, frontal; h.hy, hypohyal ; ?', jugal; in, incus; Ic, lacrymal ; mk, Meckel's 

 cartilage; ml, malleus; mx, maxilla; n, nasal; oc.c, occipital condyle ; p, 

 parietal ; pa, palatine ; ?v, premaxilla ; so, supraoccipital ; st, stapes ; s.(, 

 superior turbinal ; st.m, stapedius muscle ; sq, squamosal ; th, thyroid ; tr, 

 trachea ; V 1 , foramen for first, and V 2 for second, division of the trigeminal ; 

 //, optic foramen. 



and Primates, when the jugal is also connected with a process of 

 the frontal, 1 the orbit becomes almost completely separated from 

 the temporal fossa. 



1 Most of the true Ruminants are provided with horns projecting from the frontal 

 bones : these are of three kinds : 1, hollow horns (in the Cavicoruin) ; 2, solid 

 horns (antlers of Cervidre) ; and 3, horns of the Giraffe. 



In the Cavicornia (Boviiire, Antelopinse, Caprinse, Ovinaj) bony processes are 

 developed from the frontals, which become enveloped by horn formed from the epi- 

 dermis. In the Cervida?, a membrane bone becomes developed in the derma round 

 each process of the frontal, with which it fuses. This grows out to form the antler, and 

 after attaining its full development, the skin covering it dries up owing to the develop- 

 ment of the "burr" at its base ; this constricts the vessels, and the antler, being 

 deprived of nutriment, falls off. This occurs periodically at the close of the breeding 

 season. In the young animal, the antlers are simple, but year by year they become 

 more complicated and branched. Giraffes possess persistent antlers covered by hair 

 without any process from the frontal, which do not become anchylosed to the latter 

 bone. 



The differentiation into "horn-" and "antler-bearers" first began in the Miocene 



epocn. 



G 2 



