THE HORNY SKELETON. 239 



process is called by Kirby and Spence the medifurca ; I call it, to cor- 

 respond with the first, the processus internus mesosterni, or arcus ster- 

 nales inter ni. 



The metathorax has the most developed skeleton, and is in ge- 

 neral in the beetles the largest of the thoracic segments, whereas it 

 was the central one in the flies, butterflies, Hymenoptera, and Cicada. 

 We observe, at the metanotum, the meso- and metaphragma, two parti- 

 tions descending perpendicularly from the anterior and posterior limits 

 of this plate ; they are not very high, but to them the large dorsal 

 muscles are attached. In apterous genera (Carabus) the entire meta- 

 notum, and with it both partitions are very small. We find, besides 

 these two partitions, no other elevated process at the metanotum, 

 whereas there is a very large one at the metasternum. This originates 

 as a thin, frequently merely pergamentaceous, triangular partition from 

 its central line, and projects freely into the cavity of the thorax, but 

 with its apex more directed towards the abdomen. The thither directed 

 edge of the triangle is thicker, like a ridge ; it is placed upon its pos- 

 terior margin, and originates from the spot where both the cavities of 

 the posterior coxa? are united. When this ridge reaches the upper 

 point of the triangle it sends off on each side a strong process, which 

 together form a direct cross with the ridge itself. A third process, 

 which is, as it were, the continuation of this ridge, originates between 

 both, and runs in a direct line parallel with the carina of the sternum 

 as far as the mesothoracic segment, gradually decreasing to a point, 

 This central process is excavated above, and thus forms a smajl channel, 

 in which the intestinal canal rests. In Dyticus it even furcates, and 

 with both prongs of the fork it encloses the intestine, and lower down 

 the nervous cord. In Oryctes, however, all three processes, the two 

 transverse ones and the central one, equal both in form and size, 

 thus construct a three-rayed star ; in Hydrophilus the central process 

 is wanting, as well as in Carabus and Callichroma^ where the whole 

 frame is much smaller, and is placed between the cavities of the coxee, 

 whereas in others, at least in Dyticus and Oryctes, it projects as far as 

 the base of the abdomen. To this skeleton numerous muscles are 

 attached ; posteriorly the muscles of the coxae ; at its lateral points 

 delicate muscles, which rise to the limits of the back ; to its anterior 

 points likewise two delicate muscles, which pass through the cavities 

 of the meso- and prothorax, and affix themselves to the horny plates- 

 of the membrane of the neck (see 167. 4). Besides this large pro- 



