448 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



These changes in form are most remarkable at the spots 

 where the vessel makes sudden turns, coils, or convolutions. 

 Like a capillary, however, this vessel may divide and again 

 become single, and may send off a division to a vessel of the 

 same kind. All such divisions and anastomosing vessels, 

 however, preserve the same mean diameter, and are in this 

 respect distinguishable from arterial and venous branches. 



As regards the general arrangement of the vessels, it may 

 be observed that 



1. One vessel may enter a villus, and, returning on itself, 

 leave it again. 



2. Two vessels may enter a villus, may anastomose, and 

 leave it in one or two divisions. 



3. One or more may enter, may each separate into two 

 or more divisions, which may reunite and leave the villus as 

 they entered. 



Many other modifications occur, but the general rule is, 

 that one vessel enters and leaves the villus without dividing. 



As regards the particular arrangements of the vessels 

 within the villus, we recognise those leading varieties : 



1. The simple loop, a vessel turning closely on itself. 



2. The open loop, a vessel turning on itself, but leaving a 

 space within the loop. 



3. The wavy loop, resembling the first, except that the 

 vessel is wavy instead of being direct. 



4. The wavy open loops. 



5. The contorted loop, the contortion being generally at 

 the extremity or sling of the loop ; the limbs of the loop 

 being straight or wavy as the case may be. 



6. The various modifications which arise from combina- 

 tions of the five foregoing forms, in single, double, triple, or 

 quadruple or anastomosing loops. The most common forms 

 are the simple and contorted loop. The simple loop and the 

 wavy loop are found in cylindrical villi. The open loop and 



