THE SPHENOIDAL CONCHA 



67 



parietal, frontal, ethmoid, temporal, and sphenoidal conchse. Also with the palate, vomer, 

 zygomatic, epipteric bone when present, and occasionally with the maxilla. 



Ossification. — The sphenoid is divided, up to the seventh or eighth month of intra-uterine 

 life, into an anterior or pre-sphenoid portion, including the part of the body in front of the tub- 

 erculum sellae and the small wings, and a post-sphenoid portion, the part behind the tuberculum 

 sellae including the hypophyseal fossa and the great wings. The two portions of the body join 

 together before bii-th, but in many animals the division is persistent throughout life. 



The pre-sphenoid portion ossifies in cartilage from four centres, one of which gives rise to 

 each lesser wing (orbito-sphenoid) and a pair to the body of the pre-sphenoid. 



In the formation of the post-sphenoidal portion both cartilage and membrane bone partici- 

 pate, the pter\^goid plates being formed in membrane, while the rest of the portion, together 

 with the hamular process, ossifies from cartilage. (Fawcett.) At about the eighth week a 



Fig. 84. — The Jugum Sphenoidale. 



( 



centre appears at the base of each greater wing (ali-sphenoid), and at about the same time a 

 pair of centres appear in the body (basi-sphenoid) and later one in each lingula (sphenotic). 

 The medial pterygoid plates are pre-formed in cartilage, in which a centre appears for the 

 hamular process, but the rest of the plate is formed from membrane bone which invests the 

 cartilage. The lateral plate is formed in membrane and a considerable part of the greater 

 wing is also membranous in origin (see epipteric bone). 



At birth the bone consists of three pieces. The median piece includes the basi-sphenoid 

 and Hngulse, conjoined with the pre-sphenoid, carrying the orbito-sphenoids. 



The two lateral pieces are the ali-sphenoids, carrying the medial pterygoid plates. The 

 dorsum sellae is cartilaginous. A canal, known as the basi-pharyngeal canal, extends into the 



Fig. 85. — The Inferior Surface op Pre-sphenoid at the Sixth Year. 



Small wing 



Pre-sphenoid 



Pterygo -palatine groove 



Optic foramen 



Vidian canal 

 Vaginal process 



body from the sella turcica and sometimes reaches its under surface. It contains a process 

 of dura mater, and represents the remains of the canal in the base of the cranium, through 

 which the diverticulum of Rathke extended upward to form part of the hypophysis. 



The great wings are joined to the lingulae by cartilage, but in the course of the first year 

 bonv union takes place. About the same time the orbito-sphenoids meet and fuse in the mid- 

 dle line to form the jugum sphenoidale, which thus excludes the anterior part of the pre-sphenoid 

 from the cranial cavity. For some years the body of the pre-sphenoid is broad and rounded 

 inferiorly (fig. 85). The posterior cUnoid processes chondrify separately, a fact which throws 

 some hght on the occasional absence of these processes. 



THE SPHENOIDAL CONCHA 



The sphenoidal conchae (or turbinate bones; bones of Bertin) (figs. 86, 87) maybe obtained 

 as distinct ossicles about the fifth year, and resemble in shape two hollow cones flattened m 

 three planes. At this date each is wedged in between the under surface of the pre-sphenoid 

 and the orbital and sphenoidal processes of the palate bone, with the apex of the cone du-ected 

 backward as far as the vaginal process of the medial pterygoid plate. Of its three surfaces, 

 the lateral is in relation with the pterygo-palatine fossa, and occasionally extends upward be- 

 tween the sphenoid and the lamina papyracea of the ethmoid, to appear on the medial wall of 

 the orbit (fig. 105). The inferior surface forms the upper boundary of the spheno-palatine 

 foramen and enters into formation of the posterior part of the roof of the nasal fossa. The 



