56 MUSCULAR TISSUE. 



TEMPORARY TEETH. 



Arrangement and Time of Eruption. 



One-half only of each jaw is represented, the arrangement and time of erup- 

 tion being the same in the corresponding halves. 



Molars. Canine. Incisor. Middle line 



Second. First. Lateral. Central. of jaw. 



Upper jaw 1 1 1 1 



Time of eruption ) 



in months after I . 20-24 15-21 16-20 15-21 8-10 



birth . . . . J 



Lower jaw 1 1 1 1 



Time of eruption ) 



in months after \ . 20-24 12 16-20 15-21 6-9 



birth . . . . J 



Permanent Teeth. The second or permanent set consists of 

 thirty-two teeth, sixteen in each jaw. The third molars or wis- 

 dom teeth do not always appear. The following table gives the 

 arrangement of these teeth and the approximate time of their 

 eruption : 



PERMANENT TEETH. 



Arrangement and Time of Eruption. 



One-half only of the jaw is represented, the other half corresponding in all 

 particulars ; and as the time of eruption of the permanent teeth of the lower 

 jaw differs from that of the upper only in that it precedes it slightly, the upper 

 jaw is alone represented. 



Bicuspid or 



Third or Molar. 1'remolar. Canine. Incisor. Middle line 



Wisdom. Second. First. Second. First. Lateral. Central, of jaw. 



Upper jaw .... 1 1 1 1 111 1 | 



Time of eruption ) 



in years after 1 17-25 12 6 10 9 11 8 7 



birth . . . . J 



MUSCULAR TISSUE. 



The muscular tissue of the human body is of two kinds, volun- 

 tary and involuntary r , both being possessed of contractility or the 

 power to shorten. 



Voluntary Muscle (Fig. 49). This is composed of fibers 

 having a length of 2.5 cm. or more, and a diameter of 0.05 mm., 

 enclosed in a sheath, the sarcolemma (Fig. 48). The material 

 possessed of contractile power, contractile substance, when viewed 

 under the microscope presents the appearance of alternating dark 

 and light stripes, strive, crossing it, giving to this variety the name 

 of striated muscle. These striae are not superficial markings, but 

 are in reality the edges of dark and light disks (Fig. 49). At the 

 boundaries of the light striae are seen rows of granules, and run- 

 ning through the dark striae lines connecting the granules. These 

 lines mark longitudinally the subdivisions of the muscle, which 



