50 SPECIAL ANATOMY. 



(for the muse, pteryg, intern.), below the Indsura pteryg. (for the reception of 

 trie processus pyramidalis of the palate bones). Sometimes there is a sinus 

 pteryg. where the ala extern, and interna meet together with the Corpus sphenoid^ 

 and it is connected with the Sinus sphenoidal. (Mayer.) 



Foramen pterygo-spinosum (seu interruptum, Fitsebeck) is formed by a 

 lamella of bone, or a ligament between the proc. spinos. alte magnee and the 

 ala externa proc. pteryg. (for the ganglion oticum of Arnold). 



Texture of the Sphenoid. The compact osseous tissue pre- 

 dominates. The cavities in the commencement consist of spongy 

 bone, which, by degrees, is absorbed. 



Development. In the fetus the small wings and a portion of 

 the body are separated, even up to the ninth month, from the rest 

 of the bone (in lower animals during life, the anterior and posterior 

 sphenoids). 



Eight points of ossification. Deposit of bone first commences 

 in the large wings from the fortieth to the forty-eighth day. The 

 Cornua Bertini unite with the body of the sphenoid about the 

 fifteenth to the eighteenth year, the basilar portion in the eighteenth 

 to the twenty-fifth year. 



49. 3. Os Ethmoideum, s. cribriforme, sieve bone. 



Situation: in the central line of the anterior part of the base of 

 the skull, before the sphenoid, between the frontal bones, or rather 

 the orbital plates of the frontal bone, and behind the nasal bones. 

 Figure : that of a cube, consisting of thin bony plates. 

 Portions : 1. Central, lamina cribrosa with the lamina perpen- 

 dicularis. 



2. Lateral, two labyrinthi. 



1. Lamina cribrosa, perforated plate, horizontal, quadrangular. 



a. Superior surface, looks into the skull; from its centre a narrow, trian- 

 gular process ascends perpendicularly, the Crista Galli (for the falx cerebri), 

 with two projections on its anterior border (process, a/am) ; here is the 

 foramen-ccecum. On the sides and behind the crista, the numerous foramina 

 cribrosa (for the nerves of smell); a groove on either side, sulcus pro nerv. 

 olfadorio. 



b. Inferior surface, the uppermost wall of the nasal cavity, which is divided 

 into two by the vertically descending lamina perpendicularis. The vertical 

 plate anteriorly lies against the nasal spine of the frontal bone and the nasal 

 bones ; behind upon the crista sphenoidal., below upon the Vomer and nasal 

 cartilage. 



Borders: a. The anterior border of the cribriform plate unites with the 

 frontal bone. 



b. The posterior, with the crista sphenoidalis. 



2. Labyrinthus, the lateral portions extend directly downwards from the 

 cribriform plate, one on either side of the septum nasi, appear externally as 

 a thin plate (lamina papyracea), in the orbits, internally in the nasal cavity 

 (lamina nasalis). Between the two plates lie the cells (sinus Ethmoidaks). 



