40 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



downward from the body of the sphenoid. The broader, larger, external plate is termed the 

 external pterygoid plate, and the narrower internal one, the internal pterygoid plate, terminates 

 below in a small hook-like process, the hamular process (hamulus pterygoidcus). The pterygoid 

 process of the sphenoid tone articulates in this situation with the horizontal plate of the palate 

 bone and also with a process of this bone, its tuberosity (processus pyramidalis), which is directed 

 backward and outward and fills the gap between the external and internal pterygoid plates, 

 consequently aiding in the formation of the pterygoid jossa, which occupies the interval between 



the two plates. 



In the palate bone, at its junction with the pterygoid process of the sphenoid, there is a 

 larger anterior foramen, the greater palatine foramen, and usually several smaller posterior 

 openings, the lesser palatine foramina. 



The posterior half of the external surface of the base of the skull is formed by the two tem- 

 poral bones and by the occipital bone. All the four portions of which the temporal bone is 

 composed arc visible, namely, the inferior surfaces of the petrous portion, of the mastoid portion, 

 and of the tympanic portion, and a part of the squamous portion. The apex of the petrous 

 portion lies in an irregularly shaped opening, the foramen lacerum; it is separated from the 

 sphenoid bone anteriorly by the sphenopetrosal fissure and from the occipital bone posteriorly 

 by the petro-occipital fissure. The mastoid portion articulates with the occipital bone by means 

 of the occipitomastoid suture. 



Of the squamous portion, one sees mainly the zygomatic process (forming a portion of the 

 zygomatic arch) and the mandibular fossa, which accommodates the condyloid process of the 

 mandible and presents anteriorly the articular eminence. Of the mastoid portion, there is to 

 be seen the mastoid process (processus masloideus), which has a deep groove, the digastric fossa 

 dncisura mastoidca), upon its inner surface, and, at the side of the occipitomastoid suture, an 

 opening, the mastoid foramen. The tympanic portion, with the meatus audilorius externa s, 

 is placed between the mastoid process and the mandibular fossa, and in front of it there is a 

 fissure, the Glaserian fissure (fissura petrotympanic a). 



There are many foramina and fossae upon the very rough and irregular lower surface of 

 the petrous portion of the temporal bone. Slightly to the inner side and in front of the mastoid 

 process is the pointed styloid process; between the mastoid and styloid processes there is an 

 opening, the stylomastoid foramen; to the inner side of the styloid process there is a rather deep 

 depression, the jugular fossa, leading into the cranial cavity through an irregular opening, the 

 jugular foramen; and to the inner side and in front of the jugular fossa there is a round opening, 

 the external orifice of the carotid canal. 



The occipital bone forms the large remaining portion of the external surface of the base of 

 the skull. In the adult skull it is united with the sphenoid so that its basilar portion is continuous 

 anteriorly with the body of the sphenoid bone without demarcation. Posteriorly the basilar 

 portion forms the anterior margin of the foramen magnum, while the portions of bone external 

 to this foramen, known as the lateral portions, present the two large occipital condyles, by means 

 of which the skull articulates with the first cervical vertebra or atlas. The base of each condyle 

 is perforated by a short canal, the hypoglossal or anterior condyloid canal, while the termination 

 of a similar canal, the condyloid or posterior condyloid, is viable behind the condyle. 



