56 



THE OSTEOLOGY AND MYOLOGY 



inner side ; its outer side is in relation to the glenoid cavity and condyle of the jaw; at its 

 inner base is a large foramen, sometimes, however, only a groove continuous with the 

 foramen lacerum, from deficiency of the bony trabecule completing its periphery. | 



Perhaps the most interesting point connected with the sphenoid bone is the share it 

 takes in the formation of the glenoid cavity, by means of a long, sharp-pointed " artic- 

 ular " process of the alisphenoid, which runs along the inner and anterior margin of the 

 glenoid cavity, and usually reaches to the malar. This formation decidedlj^ augments the 

 transverse diameter of the glenoid, and a considerable part of the mandibular condyle plays 

 upon the expanded and slightly concave under surface of the sphenoidal process. The 

 latter, however, lying wholly in the general plane of the joint, does not afford an anterior 

 wall of abutment for the condyle, like that furnished behind by the downward extension of 

 the squamosal. The extent of the alisphenoid thus appropriated by the squamasal, per- 

 haps explains why so much of the sphenoparietal suture is made by the orbital plate of the 

 bone alone. This structure of the glenoid obtains in many, if not most, marsupials. 



Anteriorly the sphenoid sends off on either side a long attenuated pterapophysis, wdiich 

 diverges from its fellow as it proceeds forward. These slender prongs reach as far for- 

 ward as the termination of the bony palate ; forming the main connection of the ptery- 

 goids with the sphenoid, augmenting the connections of the latter with the palatines, and 

 forming part of the wall that laterally bounds the vestibule of the posterior nares. 



Absence of a stylo-hyal, and non-confluence of the petromastoid, leave the " temporal 

 bone " to be represented by the squamosal alone. There being but a small vacuity in the 

 cranial wall to be fdled by the squamosal, the greater part of this bone is devoted to the 

 formation of the back part of the great zygoma, and the support of the mandible. The 

 zygomatic process at first stands out at right angles with the squamous portion and then 

 curves forward, expanded vertically, to effect extensive overlapping suture with the malar. 

 The root of this process is thickened transversely for the site of the glenoid cavity; it sends 

 downward a stout process to form the posterior wall of the articulation, and presents 

 inwardly a rough, irregular projection for the alisphenoidal suture. The squamous part 

 of the bone takes but small part in the formation of the ^vall of the encephalon, and 

 less than appears upon viewing the skull outwardly, in consequence of the extent to 

 which it overlaps the parietal. The posterior border of the squamosal is somewhat thick- 

 ened and rises in a prominent ridge, which is the lateral downward continuation of the 

 semicircular occipital crest. The termination of this crest represents the postero-lat- 

 eral corner of the skull, in which the mastoid scarcely takes part, being small, and 

 wedged in between the squamosal and the ex- and par-occipitals ; separating the former 

 from the last two. Above, the squamosal comes in direct relation with the super-occipital. 

 A prominent ridge from the upper border of the zygomatic process connects the latter 

 with the squamo-occipital crest, and overarches the otocrane. The fossa in which the 

 parts of the ear lie is represented, in the lateral view, by a wide and deep notch between * 

 the glenoid process, and the termination of the occipital crest. Two large foramina are 

 situated in the notched part of the squamosal. A well marked groove, extending along 

 the inner aspect of the back part of the squamosal, is converted into a canal (venous) by 

 a corresponding groove in the surface of the closely apposed petromastoid. 



Confluence of the " mastoid process " with the otic sense-capsule results in the ji^tro- 

 mastoid, a small, hard, very irregularly shaped bone, firmly wedged in between the 



