id about the beginning of the 17th century. He entered the household
of the duke de Albuquerque, and after some years of service in the army
received the order of Santiago in 1648. He was a favourite of Philip
IV., who is reported to have collaborated with him; this rumour is not
confirmed, but there is ample proof of Coello's collaboration with
Calderon, Rojas Zorrilla, Solis and Velez de Guevara, the most
distinguished dramatists of the age. The best of his original plays,
_Los Empenos de seis horas_, has been wrongly ascribed to Calderon; it
was adapted by Samuel Tuke, under the title of _The Adventures of five
Hours_, and was described by Pepys as superior to _Othello_. It is an
excellent example of stagecraft and animated dialogue. Coello died on
the 20th of October 1652, shortly after his nomination to a post in the
household of Philip IV.

COELOM AND SEROUS MEMBRANES. In human anatomy the body-cavity or coelom
(Gr. [Greek: koilos], hollow) is divided into the _pericardium_, the two
_pleurae_, the _peritoneum_ and the two _tunicae vaginales_.

The _pericardium_ is a closed sac which occupies the central part of the
thorax and contains the heart. Like all the serous membranes it has a
visceral and a parietal layer, the former of which is closely applied to
the heart and consists of endothelial cells with a slight fibrous
backing: to it is due the glossy appearance of a freshly removed heart.
The parietal layer is double; externally there is a strong fibrous
protective coat which is continuous with the other fibrous structures in
the neighbourhood, especially with the sheaths of the great vessels at
the root of the heart, with prolongations of the fascia of the neck, and
with the central tendon of the diaphragm, while internally is the serous
layer which is reflected from the surface of the heart, where the great
vessels enter, so that everywhere the two layers of the serous membrane
are in contact, and the only thing within the cavity is a drop or two of
the fluid secreted by the serous walls. When the parietal layer is laid
open and the heart removed by cutting through the great vessels, it will
be seen that there are two lines of reflection of the serous layer, one
common to the aorta and pulmonary artery, the other to all the pulmonary
veins and the two venae cavae.

The _pleurae_ very closely resemble the pericardium except that the
fibrous outer coat of the parietal layer is not nearly as strong; it is