THE VERTEBRATE ANIMAL — SUBPHYLUM VERTEBRATA 379 



(b) Vertebral column 



1. Cervical vertebrae (neck) 



2. Thoracic vertebrae (chest) 



3. Lumbar vertebrae (small of back) 



4. Sacral vertebrae (hip) 



5. Caudal vertebrae (tail) 



(c) Thoracic basket 



1. Eibs (paired) 



2. Sternum (breastbone) 



II. Appendicular Skeleton (girdles and limbs) 



(a) Pectoral (anterior) 



1. Girdle: scapula, clavicle, procoracoid and coracoid 



2. Limb: Humerus (upper arm), radius and ulna (forearm), carpals 

 (wrist), metacarpals (palm), phalanges (bones of digits) 



(b) Pelvic (posterior) 



1. Girdle: ilium, pubis, and ischium 



2, Limb: Femur (thigh), patella (knee cap), tibia and fibula (shank), 

 tarsals (ankle), metatarsals (sole), phalanges (bones of toes) 



In Protozoa there is no very elaborate adaptation toward a skele- 

 ton. The presence of a cuticle in some and the secretion of a hard 

 shell in others seem to be the particular developments related to 

 these special functions in this group. Arcella, Difflugia, the Foram- 

 inifera, and Radiolaria exemplify this adaptation. 



The skeleton and integumentary structures serve the Metazoa 

 primarily for a support and protection. The corals of the phylum 

 Coelenterata secrete a calcareous or horny skeleton around the ex- 

 ternal surface of the body proper. The sponges, as a rule, each 

 have a calcareous, siliceous (glassy), or horny skeleton extending 

 throughout the body. Such forms as snails, crayfishes, beetles and 

 representatives of their respective phyla secrete a well-developed 

 exoskeleton as an external cover over most of the other tissues of 

 the body. The muscles and other tissues are attached within. 

 There are special cells of the epidermis which function primarily 

 in production of this skeletal material. The echinoderms, including 

 animals like the starfish, possess calcareous skeletal plates which 

 are essentially similar to exokeleton except that they are princi- 

 pally beneath the skin. 



There is no well-developed endoskeletal structure known in non- 

 chordate animals but the endophragmal structures extending into the 

 thorax of some Crustacea are thought to be the forerunner of the 

 endoskeleton. A number of exoskeletal modifications are used for 



