484 PAUL E. LINEBACK 



pig. These are all more or less adequately described in the 

 text-books of veterinary anatomy. The spiral coil in the pig is 

 clearly figured by Sisson, as seen both dissected and in situ, and 

 he adds a diagram of its course. 



The musculature of the pig's colon is also peculiar, in that it 

 possesses two taeniae instead of three throughout most of its 

 course, and it was while studying the development of these 

 taeniae that my attention was diverted to the coil itself by Dr. 

 F. T. Lewis. At his suggestion the following account of its 

 embryological history has been prepared, and it is a pleasure to 

 record my indebtedness to him for cooperating throughout this 

 work. Such an extraordinary and conspicuous formation has 

 not escaped previous study, but the existing descriptions are so 

 meager that they should certainly be supplemented by further 

 investigation. This was Martin's opinion when in 1889 he 

 pubUshed the first of his papers containing most of the informa- 

 tion now available. 



In the Schweizer-Archiv fiir Thierheilkunde Martin presents 

 a series of diagrammatic figures showing the probable evolution 

 of the spiral colon in the sheep, including hypothetical drawings 

 of some stages which he had not actually observed. They are 

 accompanied by a brief description, containing references to 

 corresponding stages in the cow, but Uttle is said regarding the 

 pig. In 1891 Martin supphed a new set of diagrams of the de- 

 velopment in the sheep, and a fuller description. In brief, he 

 considers that the colon, which previously has been quite 

 straight, forms a loop, the apex of which soon becomes bent like 

 a hook. The loop continues to elongate spirally, ''as one of its 

 limbs grows slower than the other, and thus we have the begin- 

 ning of the spiral coil." 



In the same year ('91) Bonnet pubhshed modifications of 

 Martin's earlier diagrams which are clearer, but apparently 

 more arbitrary. He records the formation of a ''primitive loop 

 of the colon" in embryos of the horse. This, he observed, has 

 become somewhat S-shaped in a specimen measuring 10 cm., 

 but it never makes more than one revolution. In the pig. Bon- 

 net finds that a corresponding loop "winds itself spirally around 



