70 



THE SKELETON 



cranium, where it forms a large part of the so-called mastoid portion of the 

 temporal bone. Besides containing the internal ear, it bears on its cranial side a 

 foramen for the seventh and eighth cranial nerves (internal auditory meatus), 

 and on its outer side two openings — the fenestra vestibuli and fenestra cochleae 

 (fig. 91). The squamosal is a superadded element and is formed as a membrane 

 bone in the lateral wall of the cranium. It is especially developed in man in 

 consequence of the large size of the brain, and forms the squamous division of the 

 adult bone, and by a triangular shaped process which is prolonged behind the 

 aperture of the ear it also contributes to the formation of the mastoid portion. 

 It is obvious, therefore, that the mastoid is not an independent element, but 

 belongs in part to the petrous, and in part to the squamous. The tympanic 

 portion, also superadded, is a ring of bone developed in connection with the 

 external auditory meatus, and eventually forms a plate constituting part of the 

 bony wall of this passage. These three parts are easily separable at birth, but 

 eventually become firmly united to form a single bone which affords little trace 

 of its complex origin. Lastly a process of bone, developed in the second visceral 

 arch, coalesces wdth the under surface of the temporal bone and forms the styloid 

 process. 



Fig. 92.— The Left Temporal Bone. (Outer view.) 



Zygomatic process 



^ 



Groove for middle 

 temporal artery 



Masseter 



Articular tubercle 

 Mandibular fossa 



Petro-tympanic fissure 



Tympanic plate 



Stylo-pharyngeus 



Stylo-hyoid 



Stylo-glossus 



Squamous portion 



>2h^ ■ Temporal muscle 



__yi>W^\ . Temporal ridge 



•/i/* K^'^%^ ^^^ Squamo-mastoid 



//^^^^f^ suture 

 *• rfMX^^ > ^ Occipitalis 



.<=.''*S«|W ' ■'^ Auricularis 



^^ anterior 



Sterno-mastoid 



Splenius capitis 



~" Mastoid foramen 



Longissimus 



capitis 

 Mastoid portion 



of temporal 



Digastric 

 Styloid process Mastoid process 



The squamous portion [squama temporalis] is flat, scale-like, thin, and trans- 

 lucent. It i.s altaciied almost at right angles to the petrous portion, forms part 

 of the side wall of the skull and is limited above by an uneven border which 

 describes about two-thirds of a circle. The outer surface is smooth, slightly 

 convex near the middle, and forms part of the temporal fossa. Above the 

 external auditory meatus it presents a nearly vertical groove for the middle 

 temporal artery. (Jonnected with its lower part is a narrow projecting bar of 

 bone known as the zygomatic process. At its base the process is broad, directed 

 laterally, and flattened from above downward. It soon, however, becomes 

 twisted on itself and runs forward, almost parallel with the squamous portion. 

 This part is much narrower and compressed laterally so as to present medial 

 and lateral surfaces with upper and lower margins. The lateral surface is sub- 

 cutaneous; the medial looks toward the temporal fossa and gives origin to the 

 maHHcier muscle. The lower border is concave and rough for fibres of the same 

 muscle, whilst the upi)er bordcjr, thin and ))r<)l()nged further forward than the 

 lower, receives the tem])()ral fascia. The extremity of the process is serrated for 

 articulation with the /ygoniatic bone. At its base the zygomatic process presents 

 three roots — anterior, middle, and posterior. 



