36 MAMMALIAN ANATOMY 



6. By its shape. 



(a) Through a resemblance, real or fancied, to some common 

 object. Examples: odontoid or tooth-like process; crib- 

 riform or sieve-like plate ; scaphoid or boat-like fossa. 



(/;) Through a resemblance to a geometrical figure. Example : 

 oval foramen. 



7. By a peculiarity of texture. Examples: petrous or rock-like 



portion of the temporal bone, linea aspera, rough line. 



8. By its function, real or fancied. Example : nutrient canal. 



9. By the name of an anatomist, not necessarily the name of that 



anatomist who first discovered it. Examples : hiatus Fallopii 

 (Fallopius, A.D. 1523-1562), Glaserian fissure (Glaser, A.D. 

 1629-1675). 



DEVELOPMENT OF BONES. 



The greater part of the skeleton is preformed in cartilage, in such 

 a manner that every original cartilaginous element lias the form of the 

 bone which is to develop in and about it. A few bones, however 

 (almost exclusively bones of the skull), are not first formed in car- 

 tilage, but are developed independently in or from membranes. Bones 

 of the first class are said to have an intracartilaginous development ; 

 those of the second class, an intramembranous development. 



Ossification is not merely the deposit of lime salts in the carti- 

 laginous or membranous matrix, it is a total transformation of the 

 existing tissues into bone tissue by means of special cells termed osteo- 

 blasts. 1 It always begins in a primary centre which is more or less 

 central, and there may be no other centres. In most bones, however, 

 secondary centres (Fig. 12) appear at the ends or in special parts 

 and coalesce with the primary centre, sometimes almost immediately, 

 sometimes not until adult life. As has been already pointed out, the 

 primary centre of long bones is in the diaphysis, the secondary centres 

 are in the epiphyses. 



GEOWTH OF BONES. 



Bones grow by the deposit of new bone material upon that already 

 formed, so-called appositional growth, and not by the interposition of 

 new bony molecules between the molecules already present, so-called 



1 From (Gr.) osteon, bone, and blastos, A germ. 



