in.] THE CRANIAL SKELETON-. 81 



which is at birth separate from a little cylindrical piece of 

 bone which afterwards forms its root, and which is called 

 the tympano-hyal. 1 



Besides these three elements, three other distinct ossifica- 

 tions extend and coalesce to form the petrous and mastoid 

 portions of the temporal bone, and are distinguished by their 

 diverse relations to parts of the internal organ of hearing. 

 Continuing our enumeration, we have (4) an ossification which 

 gives rise to the upper part of the petrous portion (that which 

 is visible on the inside of the skull) and to part of the mastoid. 

 It forms the upper margin of what will hereafter be noticed 

 as the fenestra ovalis- of the internal ear, and is especially 

 related to the anterior vertical semicircular canal. It is called 

 the pro-otic.* (5) One which gives rise to the lower part of 

 the petrous portion (that which is visible on the base of the 

 skull) and forms the carotid canal. It also forms the lower 

 part of the fenestra ovalis, and surrounds entirely what is 

 termed the fenestra rotunda. It is called the opisthotic.* 

 (6) One which gives rise to the mastoid process, and which 

 is developed upon the posterior part, and what we shall here- 

 after know as the posterior vertical semicircular canal of the 

 internal ear. It is called the epiotic'.f The mastoid process 

 is not prominent at birth. 



6. The SPHENOID 6 is a very complex bone, and has been 

 likened to a creature with a small body, two pairs of wings, 

 and two legs. 



The central part, or body (which is anchylosed with the 

 basilar part of the occipital), has on its upper surface a 

 deepish pit, called \h&sella turcica or pituitary fossa, because 

 it receives the pituitary body of the brain. It is bounded 

 behind by a vertical plate, termed "clinoid," 7 from the 

 summit of which projects on each side a " clinoid process. 



From each side of the body there projects upwards, out- 

 wards, and forwards a large more or less triangular plate, 

 called the greater a/a, or wing of the sphenoid, which also 

 sends a lamellar process downwards. At the root ot t 

 wing are three holes. The innermost and smallest the 

 vidian transmits the vidian nerve. Above and external t 



' Discovered and named by Professor Flower ( Osteology/' p. 123}. Every 

 bone connected with the tongue-bone, or hyoid, has the term hyal as a part 



itS *Th C as also been noticed in the Eighth Lesson of " Elementary Physiology." 

 3 n p 6, before and ov S , irog, the ear. , ^^ 



6 K&JSSSrtr, a wedge, and efcoc, like. 7 From *J* a bed. 



G 



