2i 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



From the upper end of the hiatus a bud of mucous membrane 

 grows upwards to form the frontal sinus, gradually works through 

 the ethmoid, and pushes its way into the frontal bone, separating 



infundibulum 

 ant. ethm. sinus 

 mid. ethm. sinus 



lachrymo-ethmoicl. 

 naso-turbinal. 

 hiatus semilunaris 



vestigial turbinates 

 post. ethm. sinus 

 ^sphen. sinus 

 sphen. turb. 



Eustachian tube 



lateral recess 

 of pharynx 



Flc. 19. — A diagram of the Lateral Wall of the Nasal Cavity, showing the position of 

 the Air Sinus. The parts beneath the turbinate processes are indicated by 

 stippled lines. 



the outer from the inner lamellae. As a rule, by the 25 th year 

 it reaches outwards over the inner two-thirds of the orbital roof, 

 and is an inch or more both in height and depth at its inner part. 

 It is smaller in women than in men, but it may be, and often 

 is, arrested at an early stage of development, or it may be absent 

 altogether. The size of the glabellar prominence is no index to 

 its development. 



The stalk of the frontal bud forms the infundibulum, which is 

 narrow, half an inch long, and difficult of catheterization from the 

 nose. Into it open (or sometimes into the hiatus) the lachrymo- 

 ethmoidal and anterior ethmoidal cells which surround the infundi- 

 bulum. They are developed as outgrowths from the infundibulum 

 (Fig. 19). Occasionally the antrum of Highmore, as is frequently 

 .the case in the gorilla, sends a process to form part of the frontal 

 sinus, and hence there may be a communication between the sinus 

 and the antrum. 



The development of the frontal sinuses and supra-orbital ridges 

 lead to a marked change in the face at puberty. By the forma- 

 tion of the frontal sinuses the basal area of the skull, to which 

 the face is attached, is largely increased in extent. Such an 



