ANATOMY IX A NUTSHELL. oil 



The superior bordeb of the squamous portion is thin and overlaps the 

 parietal bone. 



The antebo-infebiob border is thick and articulates with the greater wing 

 of the sphenoid bone. 



The mastoid portion of the temporal bone projects like a nipple from the 

 inferior portion of the bone posteriorly. 



The outer surface of the mastoid process has attached to it the Occipito- 

 frontalis muscle near the Retrahens aurem. The mastoid foramen may be on 

 this part of the bone but is often on the occipital bone. It transmits a vein to 

 the lateral sinus and a meningeal branch of the occipital artery. There are 

 numerous small foramina on this surface. 



The inner surface of the mastoid process has a deep curved fossa for the 

 lateral sinus. This process gives attachment to the following muscles. (1) 

 Sterno-cleido-mastoid. (2) Splenitis capitis. (3) Trachelo-mastoid, (4) Digastric, 

 (5) Retrahens aurem, (6) Occipito -frontalis. 



The digastric fossa is on the inner side of the mastoid process. The occipital 

 groove, which is for the occipital artery, lies parallel to the digastric fossa in- 

 ternally to it. The mastoid cells are situated in the mastoid process and open 

 into the tympanum. They are lined with mucous membrane. The upper ones 

 are large, while the lower ones are small. 



The superior border of the mastoid portion articulates with the pos- 

 terior angle of the parietal. 



The posterior border articulates with the occipital bone between it- 

 jugular process and lateral angle. 



The petrous portion of the temporal bone is of a pyramidal form and i- 

 situated between the sphenoid bone and the occipital bone. This portion of 

 the bone is very dense and hard. It contains the internal and middle ear and 

 passes forward and inward. It has a base, an apex, three surface.-, and three 

 borders. 



The base is situated against the squamous and mastoid portions, the lower 

 half of this base can be seen between the divergence of the squamous and mas- 

 toid portions, but the upper half is concealed by them. The base presents the 

 following points: 



The meatus auditobius extebnus, which is the external opening of the 

 ear. This opening lies in front of the mastoid process between the posterior 

 root and middle root of the zygoma. The upper margin of this opening is 

 smooth and belongs to the squamous portion of the temporal bone. but the rest 

 of it belongs to the petrous portion of the temporal bone and forms the second 

 point for consideration at the base of the petrous portion, namely, the m di- 

 TORY process which is for the attachment of the cartilage of the ear. 



The apex, which lies internally at the base of the skull, is received betw< 

 the greater wing of the sphenoid and the basilar process of the occipital bone. 

 thus forming the outer boundary of foramen lacerum medium, and contain- the 

 internal carotid canal. 



The anterior surface of the petrous portion of the temporal bone form- the 

 back part of the middle fossa of the skull and i> united with the squamous 



