GENERAL MORPHOLOGY OF THE BONES OP THE HEAD. 



79 



cranium and its strong crests of bone, the larger projecting face and jaws, and the other 

 characteristic features of the skull in most animals. 



As regards the condition of the individual bones, it is farther to be remarked that there is 

 generally in the human skull a more complete consolidation or bony union of the osseous 

 elements than in animals, so that the whole number of bones forming the cranium and face 

 is least in man. Thus, to mention only some of the most marked examples of this difference 

 among mammals ; the frontal bone and the lower jaw frequently divided into two lateral 

 portions ; the premaxillary very generally a separate bone from the maxillary ; the presphenoid 

 in many separate from the postphenoid j the interparietal from the occipital ; and the 

 squamosal and styloid ossifications from the periotic. It is also worthy of observation that 

 the conditions now referred to as permanent in animals exist as transitory stages of develop- 

 ment in man. 



Homologles. It is not possible here to enter at any length into the consideration of the 

 homologies of the bones of the human skull, but the diagrammatic representation of the bones 

 of the foetal head in fig. 82, and the following table will serve to indicate to some extent the 



Fig. 82. DIAGRAMMATIC VIEW 



OP THE BONES IN THE RIGHT 

 HALF OF A FCETAL SKULL, 

 FROM THE INSIDE. (Allen 



Thomson. ) 



In this figure the bones have 

 been slightly separated and dis- 

 placed so as to bring the whole 

 into one view : f, frontal ; pa, 

 parietal ; so, supraoccipital ; 

 n, nasal ; I, lachrymal ; ma, 

 malar ; os, orbitosphenoid ; 

 ris, alisphenoid ; sq, squa- 

 mosal ; zy, zygomatic ; per, 

 periotic ; eo, exoccipital ; et, 

 ethmoturbinal ; tnx, maxilla ; 

 mt, maxilloturbinal ; pm, pre- 

 maxillary ; me, mesethmoid ; 

 v, vomer ; pi, palatal ; pt, 

 pterygoid ; j)s, presphenoid ; 

 bs, basisphenoid ; bo, basioc- 

 cipital ; c, bodies of 2nd, 3rd, 

 and 4th cervical vertebrae ; c', 

 odontoid process ; x , anterior 

 arch of atlas ; s, spinous pro- 

 cesses of 1st, 2nd, 3rd, and 

 4th cervical vertebrae ; cm, 

 neural canal ; ch, a line indi- 

 cating the position of the 

 notochord passing through the 

 vertebral bodies into the base 

 of the cranium ; ty, tympanic, 

 along with ml, i, and st, dis- 

 placed from its connection with 



per ; ml, malleus ; c. ink, cartilage of Meckel ; mn, mandible ; ?', incus ; st, 

 ch, ceratohyal ; th, tHyrohyal ; bh, basihyal ; t, thyroid cartilage. 



stapes ; sth, stylohyal ; 



morphological relations of the several bones to each other, and to those of other vertebrate 

 animals, and to explain the origin of the constituent elements of the skull. Additional 

 information as to the latter point will be found in the account of the development of the head 

 in the chapter on Embryology in Vol. I. ; and for a fuller explanation of the homologies of the 

 bones the reader is referred to works on Comparative Anatomy. 



LIST OF THE TYPICAL COMPONENT PARTS OF THE BONES OF THE HEAD 

 CLASSIFIED ACCORDING TO THEIR ORIGIN l : 



1. BONES DEVELOPED IN THE PRIMITIVE CARTILAGINOUS CRANIUM. 

 Basioccipital ; Basilar process of the occipital bone. 

 Exoccipitals ; Condylar portions of the occipital bone. 

 Supraoccipital ; Lower division of the tabular part of the occipital bone. 



1 The names first given, and printed in black type, are those received in comparative anatomy ; 

 those usually employed in human anatomy follow, and are printed in common type. 



