122 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



The most posterior of these bones is the cihmoturbinal or ethmoid labyrinth sit- 

 uated just in front of the cribriform plate. It is a greatly folded structure, the 

 folds inclosing spaces known as the ethmoid cells. In front of the ethmoturbinal 

 is another but smaller mass, the maxilloturbinal, borne on the inner surface of 

 the maxilla. Each nasal bears on its inner surface a single elongated ledge of 

 bone, which constitutes the nasoturbinal, and which lies above the uppermost 

 scrolls of the ethmoturbinals. The function of the turbinals is to increase the 

 respiratory and olfactory surface of the nose. The ethmoturbinals are covered 

 by the olfactory epithelium, while the maxilloturbinals serve to strain and moisten 

 the air. The latter will be seen to project into the passage from the anterior to 

 the posterior nares. 



From the comparative standpoint the septum of the nose is the mesethmoid, 

 the perpendicular plate of the ethmoid being its ossified portion, while the ethmoid 

 labyrinths are the ectethmoids. The cribriform plate is produced by the exten- 

 sion of ossification processes between the mesethmoid and ectethmoids. The 

 perforations in the plate are for the passage of the olfactory nerve. Thus, the 

 three ethmoid bones of lower vertebrates are fused into the single ethmoid bone 

 of mammals. 



Draw the sagittal section. 



9. The foramina of the skull. — The skull is pierced by numerous openings for 

 the passage of nerves and blood vessels and sometimes other structures. These 

 are listed below for convenient reference. 

 Cat: 



a) Incisive foramina. Anterior end of ventral side of maxillae; connect roof 

 of mouth with nasal cavities. 



b) Infraorbital foramen. Large opening in the maxilla at the beginning of 

 the zygomatic arch ; for the passage of certain branches of the fifth cranial nerve 

 and blood vessels. 



c) Nasolacrimal canal. Anterior end of the lacrimal bone and passing 

 through the maxilla into the nasal cavities; for the draining of the tears. 



d) Sphenopalatine foramen. In that part of the palatine bone which extends 

 into the orbit, posterior to the lacrimal; for the passage of branches of the fifth 

 nerve into the nasal cavity. 



e) Posterior palatine canal. The posterior end of this is immediately ventral 

 to the sphenopalatine foramen; its anterior end is in about the middle of the 

 palatine process of the maxilla; for the passage of a branch of the fifth nerve 

 to the palate. 



/) Optic foramen. In the orbitosphenoid part of the presphenoid, in the 

 posterior part of the orbit, most anterior of a row of four foramina; for the 

 passage of the optic nerve. 



g) Orbital fissure. Second and largest of the row of four; through it pass the 

 third, fourth, and sixth nerves to the muscles of the eyeball, and a part of the fifth. 



