THE SPHENOID BOXE 



89 



the squamous during the first year, and the tympanohyal portion of the styloid process about 

 the same time (Figs. 54 and 55). The stylohyal does not join the rest of the bone until after 

 puberty, and in some skulls never becomes united. The subsequent changes in this bone are, 

 that the tympanic plate extends outward and backward, so as to form the meatus auditorius. 

 (1) The extension of the tympanic plate, however, does not take place at an equal rate all around 

 the circumference of the ring, but occurs most rapidly on its anterior and posterior portions, 

 and these outgrowths meet and blend, and thus, for a time, there exists in the floor of the meatus 

 a foramen, the foramen of Huschke; this foramen, usually closed by the fifth year, may persist 

 throughout life. (2) The glenoid cavity is at first extremely shallow, and looks outward as 

 well as downward; it becomes deeper and is ultimately directed downward. Its change in direc- 

 tion is accounted for as follows: the part of the squamous temporal which supports it lies at first 

 below the level of the zygoma. As, however, the base of the skull increases in width, this lower 

 part of the squama is directed horizontally inward to contribute to the middle fossa of the skull, 

 and its surfaces therefore come to look upward and downward. (3) The mastoid portion is 

 at first quite flat, and the stylomastoid foramen and rudimentary styloid process lie immediately 

 behind the tympanic ring. With the development of the air cells the outer part of the mastoid 

 portion grows downward and forward to form the mastoid process, and the styloid process 

 and stylomastoid foramen now come to lie on the under surface. The descent of the foramen 

 is necessarily accompanied by a corresponding lengthening of the aqueduct of Fallopius. 



Squamous portion 



Petrosquamous 

 suture 



Squamous portion 



Petrosquamous suture 

 Eminentid arcuafa 



Tympanic 

 ring 



Petromastoid 

 portion 



FIG. 54. Temporal bone at birth. Outer aspect. 



Fossa subarcuata, 



Meatus acusticus internus 

 FIG. 55. Temporal bone at birth. Inner aspect. 



(4) The downward and forward growth of the mastoid process also pushes forward the tympanic 

 plate, so that the portion of it which formed the original floor of the meatus and containing 

 the foramen of Huschke is ultimately found in the anterior wall. (5) With the gradual increase 

 in size of the petrous portion the floccular fossa or tunnel under the superior semicircular canal 

 becomes filled up and almost obliterated. 



Articulations. With Jive bones occipital, parietal, sphenoid, mandible, and malar. 



Attachment of Muscles. To fifteeen to the squamous portion, the Temporal; to the 

 zygoma, the Masseter; to the mastoid portion, the Occipitofrontalis, Sternomastoid, Splenius 

 capitis, Trachelomastoid, Digastric, and Posterior auricular; to the styloid process, the Stylo- 

 pharyngeus, Stylohyoid, and Styloglossus; and to the petrous portion, the Levator palati, Tensor 

 tympani, Tensor palati, and Stapedius. 



The Sphenoid Bone (Os Sphenoidale). 



The sphenoid bone is situated at the anterior part of the base of the skull, 

 articulating with all the other cranial bones, which it binds firmly and solidly 

 together. In its form it somewhat resembles a bat with its wings extended; and 

 is divided into a central portion or body, two greater and two lesser wings extending 

 outward on each side of the body, and two processes the pterygoid processes 

 which project from the lower part of this body. 



