178 



VERTEBRATE SKELETON 



forated for the lacrimal duct and orbital gland, which led to its being 

 regarded as a lacrimal, but it is probably the homologue of the rep- 

 tilian prefrontal, although it may contain supraorbital elements. 

 Supraorbitals, as one or more distinct bones, are present in several 

 birds (Rap tores, some fowl, crane, ostrich, Tinamus and Arboricola 

 have several) loosely attached to frontal or prefrontal. Some birds 

 have an infraorbital adjoining the zygomatic or descending process 

 of the prefrontal. 



The squamosal, on the anterolateral otic region, forms a part of 

 the cranial and usually of the postorbital wall. It often has a 

 descending process which separates orbit and temporal fossa and 

 (some parrots) continues forwards, bounding the orbit below. It 

 is peculiar in not connecting with the zygomatic arch. 



Fig. 192. — Cranium of young Buteo (Biitschli, '10); cartilage stippled, as, ali- 

 sphenoid; bs, basisphenoid; eo, exoccipital; /, frontal; I, lacrimal; me, mesethmoid; mx, 

 ma.xilla; n. nasal; na, naris; ors, orbital septum; p, parietal; pi, palatine; pm, premaxilla; 

 q. quadrate; qj, quadrate jugal; r, rostrum; so, supraoccipital ; sq, squamosal; s, zygo- 

 matic; 2, exit of optic nerve. 



Birds never have the closed palate of many reptiles (fig. 189). 

 The parasphenoid arises on the lower hinder part of the cranium by 

 three centres, one a little in front of the hypophysial fenestra, the 

 paired centres being ventral to the lateral parts of the basal plate 

 and otic capsules, these latter forming the bone formerly called the 

 basitemporal. The anterior part closes the hypophysial fenestra 

 and fuses with the presphenoid, forming the rostrum. It also fuses 

 with the ba.sitemporal parts which unite so firmly with the basisphen- 

 oid that they cannot be separated. 



The vomer, variable in size (sometimes absent, and small except 

 in Ratites) arises from paired centres, the two halves remaining 

 separate in Picidie. It lies on the lower side of the interorbital 



