38 



THE BONES. 



tuberosities placed on each side of the perpendicular lamina, and offering 

 for study a middle portidk, a base, and a summit. Each of these is formed by 

 an assemblage of numerous, extremely thin, osseous plates, curved into 

 small and very fragile convolutions. These, elongated from above to below, 

 become longer as they are more anterior ; they are attached by their superior 

 extremities to the transverse plate which separates the cranium from the 

 nasal cavities, and by one of their borders to a thin leaf of bone which 



envelops the lateral masses out- 

 wardly. They have received the 

 name of the ethmoidal volutes (or 

 cells). 



Middle portion. This should 

 be studied externally and inter- 

 nally. 



^e ex ^ erna ^ surface of each 

 ethmoidal mass is divided into two 

 sections: an internal, making 

 part of the nasal cavities ; the 

 other, external, concurs in form- 

 ing the walls of the frontal and 

 maxillary sinuses. The first, the 

 least extensive, is almost plane; 

 parallel to the perpendicular la- 

 mina, it is isolated from it by the 

 narrow space which forms the 

 bottom of the nasal cavities ; it 

 presents several openings which 

 separate the most superficial cells, 

 and join the internal canals to be 

 hereafter noticed. The second, 



A, Occipital bone. 1, Condyle ; 2, Con- 

 dyloid foramen ; 3, Styloid process j 

 4, Summit of basilar process. B, Parie- 

 tal bone. 8, Parietal protuberance; 

 9, Channel which concurs to form the 

 parieto-temporal canal. C, Frontal 

 bone. 10, Transverse crests separating 

 the cranial from the facial portion of 

 the bone; 11, Frontal sinuses; 12, 

 Notch on the lateral border occupied 

 by the wing of the sphenoid bone ; 13, 

 Notch for the formation of the orbital 

 foramen; 14, Summit of the orbital 

 process ; 15, Supraorbital foramen. 

 D, Perpendicular lamina of the ethmoid 

 bone. E, E, Lateral masses of the eth- 

 moid bone. 16, The great ethmoid cell. 

 F, Squamous portion of the temporal 

 bone. 17, Supercondyloid process ; 

 18, Channel for the formation of the 

 parieto-temporal canal. G-, Tuberous 

 portion of the temporal bone. 5, Mas- 

 toid process; 6, Internal auditory 

 hiatus ; 7, Opening for the eustachiau 

 ANTERIOR BONES OF THE HEAD OF A FCETUS tube into the tympanum. H, Lach- 

 (HORSE) AT BIRTH ; DISARTICULATED, AND rymal bone. i, 'Nasal bone. J, Su- 

 VIEWED FROM BEHIND. perior turbinated bone. 



