278 OSTEOLOGY. 



of its occurrence in Peruvian skulls, the os Incce. By a reference to the account of the ossi- 

 fication of the bone, the occurrence of this anomaly is explained developmentally. In 

 place of forming a single bone the interparietal is occasionally met with in two symmetrical 

 halves, and instances have been recorded of its occurrence in three or even four pieces. In 

 the latter cases the two anterior parts form the pre-interparietals. Not uncommonly the 

 internal occipital crest is split and furrowed close to the foramen magnum for the lodgment of 

 the vermis of the cerebellum, and is hence called the vermiform fossa. Instances are 

 recorded of the presence of a separate epiphysis between the basi-occipital and the sphenoid, 

 the os basioticum (Albrecht) or the os pre-basi-occipitale. An oval pit, the fovea bursse or 

 pharyngeal fossa, is sometimes seen in front of the tuberculum pharyngeum. This marks the 

 site of the bursa pharyngea. Occasionally the basilar part is pierced by a small venous 

 canal. The articular surface of the condyles is sometimes divided into an anterior and posterior 

 part. The so-called third occipital condyle is an outstanding process arising from the anterior 

 border of the foramen magnum, the extremity of which articulates with the dens of the 

 epistropheus. Guerri has recorded a case, in which in a fostal skull, there were two projecting 

 tubercles in the position of the third occipital condyle, independent of the basi-occipital portions 

 of the condyles. (Anat. Anz. vol. xix. p. 42.) This appears to confirm the view of Macalister 

 that there are two different structures included under this name one a medial ossification in 

 the sheath of the notochord, and the second, a lateral, usually paired process, caused by the 

 deficiency of the medial part of the hypochordal element of the hindmost occipital vertebra, 

 with thickenings of the lateral parts of the arch. Springing from the under surface of the 

 extremity of the jugular process, a rough or smooth elevated surface, or else a projecting process, 

 the extremity of which may articulate with the transverse process of the atlas, is sometimes 

 met with. This is the paroccipital or paramastoid process. The size and shape of the foramen 

 magnum varies much in different individuals and races, as also the disposition of its plane. 

 Elliot Smith has called attention to the asymmetry of the cerebral fossae, which is correlated 

 with asymmetry of the occipital poles of the cerebral hemispheres. Numerous instances of fusion 

 of the atlas with the occipital bone have been recorded. Many are, no doubt, pathological in 

 their origin ; others are associated with errors in development. Interesting anomalies are those 

 in which there is evidence of the intercalation of a new vertebral element between the atlas and 

 occipital, constituting what is termed a pro-atlas. 



Temporal Bone. The occurrence of a deficiency in the floor of the external acoustic meatus 

 is not uncommon in the adult. It is met with commonly in the child till about the age of five, 

 and is due to incomplete ossification of the tympanic plate. The line of the petro-squamosal 

 "suture is occasionally grooved for the lodgment of a sinus (petro-squamosal) ; sometimes the 

 posterior end of this is continuous with a canal which pierces the superior border of the bone 

 and opens into the transverse sinus. Anteriorly the groove may pass into a canal which pierces 

 the root of the zygoma and appears externally above the lateral extremity of the petro- tympanic 

 fissure. These are the remains of channels through which the blood passed in the foetal condition 

 (see ante). Kazzander has recorded a case in which the squamous part of the temporal was 

 pneumatic, the sinus reaching as high as the parietal and the squamoso - sphenoidal suture. 

 Symington has described a case in which the squamous part was distinct and separate from 

 the rest of the temporal bone in an adult; whilst Hyrtl has observed the division of the 

 squamous part of the temporal into two by a transverse suture. The zygomatic process has been 

 observed separated from the rest of the bone by a suture close to its root (Adacni). P. P. Laidlaw 

 (Journ. Anat. and Physiol. vol. xxxvii. p. 364) describes a temporal bone in which there was 

 absence of the internal acoustic meatus and of the stylo-mastoid foramen. The jugular fossa 

 also was absent, and there was partial absence of the groove for the transverse sinus, associated with 

 the presence of a large mastoid foramen. An instance of a rudimentary condition of the carotid 

 canal is also referred to in the same volume by G. H. K. Macalister. 



G. Caribbe (Anat. Anz. vol. xx. p. 81) notes the occurrence in idiots and imbeciles of a more 

 pronounced form of post-glenoid tubercle, and associates it with regressive changes in the develop- 

 ment of the temporal bone. 



Sphenoid. Through imperfect ossification the foramen spinosum and foramen ovale are 

 sometimes incomplete posteriorly. Le Double (Bull, et mtm. de la Soc. d'Anth. de Paris, 5 e se"r. 

 vol. iii. p. 550) records a case in which the foramen rotundum and the superior orbital fissure 

 were united so as to form a single cleft. 



Through deficiency of its lateral wall, the optic foramen, in rare instances, communicates 

 with the superior orbital fissure. Duplication of the optic foramen is also recorded as a rare 

 occurrence, the artery passing through one canal, the nerve through the other. Persistence of 

 the cranio- pharyngeal canal is also occasionally met with. Owing to the ossification of fibrous 

 bands which frequently connect the several bony points, anomalous foramina are frequently 

 met with. Of such are the carotico-.clinoid formed by the union of the anterior and middle 

 clinoid processes, the pterygo-spinous foramen enclosed by the ossification of the ligament con- 

 necting the angular spine with the lateral pterygoid lamina, and the porus crotaphitico- 

 buccinatorius similarly developed by the ossification of ligament immediately below and lateral 

 to the inferior aperture of the foramen ovale. 



Ethmoid. The size of the lamina papyracea is liable to considerable variations. In the lower 

 races it tends to be narrower from above downwards than in the higher, in this respect resem- 

 bling the condition met with in the anthropoids. The lamina papyracea may fail to articulate 

 with the lacrimal owing to the union of the frontal with the frontal process of the maxilla 



