50 



tthiiwidal, is i'nrnied by a very thin platr 

 of compact tissue, fragile and like ]i:i]>yni<. 

 fixed by its anterior border to the internal 

 crest of the nasal bone, and rolled on 

 itself, from before to behind, in tbo same 

 iniinner as the cells of the ethmoid bone. 

 Above, it is confounded with the last- 

 named bone, of which it is only, properly 

 speaking, the most anterior volute. At its 

 inferior extremity, it is prolonged by a 

 fibro-cartilaginous framework to the ex- 

 ternal orifice of the nose. 



Its internal cavity is partitioned by a 

 transverse plate into two portions: the 

 superior compartment forms part of the 

 frontal sinus ; the inferior is subdivided by 

 other small lamellae into a variable number 

 of cells which communicate with the nasal 

 cavity. This bone, developed from a 

 single nucleus, is ossified at the same time, 

 and in the same manner, as the ethmoidal 

 cells. Before birth, it is already intimately 

 consolidated with the nasal bone. 



The posterior, inferior, or ma-rillnri/ 

 turbinated bone resembles the first, except 

 in some particulars. Thus, its bony or 

 proper portion is not so long or volu- 

 minous, while its cartilaginous part is, on 

 the contrary, more developed. It is at- 

 tached, by its posterior border, to the vor- 

 tical and sinuous crest of the super- 

 maxillary bone, and is rolled from behind 

 to before, or in an inverse direction to the 

 other. It has no connection with the 

 LOXGITUDINAL AND TRAxsvKRSK SEC- ethmoid, and its superior cavity forms 

 TIOX OF THE HORSE'S HKAD, SHOW- part of the i n f cr i or mftX iHary sinus. It 



ss, ^nr-^rs^s w *? T-? M. * - -** 



MAXILLARY SINUSES. united in a definite manner to the max- 



1, Condyloid foramen; 2, Section of the illary bone until the horse is about a year 

 parieto-temporal canal ; 3, Occipito- old. 



spheno-temporal hiatus; 4, Carotid The mcatuses are distinguished into 



3$LJL^^-tc: anterior or superior middle, ^posterior 



fissure ; 5, Origin of the supersphe- or inferior. The first passes along the 



noidal canals. c, Sella turcica ; 6, front of the ethmoidal turbinated bone; 



Optic fossa; 7, Portion of the the second separates the two turbinated 



crista-galli process; 8, Cribriform b d ^^^ near itg . 



plate of the ethmoid bone; 9, Per- ' . ,, r '. . r . 



Pedicular plate of the same bone; extremity, the opcnm- <-onn.mnicatmg 

 in, 10, Its lateral masses; 11. Inte- between the sinuses and the nasal cavi- 

 rior of the great ethmoidal cell ; IL', 



12, Bottom of the maxillary sinuses communicating with the sphenoM.il .sinuses; 1.'*, Supe- 

 rior maxillary sinus; 14, Inferior maxillary sinus; 14', Superior compartment of the max- 

 illary turbinated bone, forming part of the latter sinus; 15, Section of the snpermaxillo- 

 dental can.il ; 1, Channel of the vomer; 17, Internal pro<--s, or jmint of thn premax- 

 illary bone. 



